Year 10 Maths · Unit 2 · Lesson 12

Word Problems with Linear Equations

Translate real-world situations into equations, solve them systematically, and check that your answers make sense.

40 min 8 cards 130 XP
Word Problem 2 adults, 3 kids Total: $60 Equation 15a + 10c = 60 a + c = 4 Real world check Answer makes sense
Think First
warm-up

A movie ticket costs $15 for adults and $10 for children. A family of 2 adults and 3 children pays a total. How much do they pay? Now, if you only knew the total was $60 and there were 4 people, how could you work backwards?

Record your answer in your workbook.
1
The Big Idea
+5 XP to read

Word problems are just equations wearing a disguise. The key is to read carefully, define one variable, express everything in terms of that variable, write an equation, solve it, and check that the answer makes sense. Every word problem can be broken down into these steps.

ReadDefineWrite → Solve → Check

1. Read the problem 2. Define the variable 3. Write the equation 4. Solve 5. Check
systematic approach
2
Lesson Objectives
what you will learn
  • Translate word problems into linear equations
  • Solve problems involving consecutive numbers
  • Set up and solve money and pricing problems
  • Solve distance, speed and time problems
  • Verify answers by checking against the original problem
3
Key Vocabulary
terms to know
VariableA letter used to represent an unknown quantity in an equation.
Consecutive integersWhole numbers that follow each other in order: n, n+1, n+2...
Consecutive even/oddEven or odd numbers that follow each other: n, n+2, n+4...
Flag fallA fixed starting charge, e.g. a taxi fee before any distance is travelled.
Relative speedThe speed of one object compared to another, used in catch-up problems.
Systematic approachA step-by-step method: read, define, write, solve, check.
4
Spot the Trap
heads-up

Wrong: Using two different variables for related quantities without connecting them. For example, using x and y for two consecutive numbers without stating y = x + 1.

Right: Express all unknowns in terms of a single variable. If the first number is n, the next consecutive number is n + 1.

Wrong: Forgetting to check if the answer makes sense. Getting a negative age or a fractional number of people.

Right: Always ask: "Does this answer make sense in the real world?"

5
A Systematic Approach
+5 XP

Every word problem can be solved with the same five-step process. Skipping a step invites errors. Rushing to write the equation before understanding the problem is the most common cause of wrong answers.

ReadDefineWrite → Solve → Check

1. Read carefully 2. Define the variable 3. Write the equation 4. Solve 5. Check and state answer
never skip a step
Read twice
Read the problem once to understand, then again to identify the numbers and relationships.
Define clearly
Write "Let n = ..." in full sentences. It earns marks and keeps you focused.
Check with words
Plug your answer back into the original sentence, not just the equation.
6
Consecutive Numbers
+5 XP

Consecutive integers follow each other: n, n+1, n+2. Consecutive even or odd numbers are two apart: n, n+2, n+4. Always express every unknown in terms of one variable. This gives you one equation with one unknown.

Sum = 54: $n + (n+2) = 54$$n = 26$.

n + (n+2) = 54 2n + 2 = 54 n = 26, 28
one variable only
Odd or even?
Consecutive even/odd numbers are 2 apart, not 1. Read the problem carefully.
Write the full list
After finding n, state all the numbers explicitly: 26 and 28, not just n = 26.
Check the sum
Add your numbers back up. 26 + 28 = 54. If it matches, your answer is correct.
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Money and Pricing Problems
+5 XP

Money problems involve fixed costs (flag falls, base fees) and variable costs (per item, per kilometre). Write one equation for the total quantity and another for the total cost. Substitute to solve. Always convert all amounts to the same unit before solving.

$22 adults, $14 kids, $152 total, 10 people.

a + c = 10 22a + 14c = 152 a = 4, c = 6
same units first
Two equations
One for quantity, one for cost. Use substitution to combine them.
Convert to one unit
All dollars or all cents. Do not mix units in the same equation.
Check both totals
Verify the number of items AND the total money both match.
8
Distance, Speed and Time
+5 XP

The formula d = rt (distance = rate � time) is the foundation of all motion problems. In catch-up problems, the faster object covers the same distance as the slower one, but starts later. Set the distances equal and solve for time.

Train 90 km/h at 9am. Car 120 km/h at 10am. When does car catch up?

90 + 90t = 120t 90 = 30t t = 3, 1:00 pm
set distances equal
Head start matters
Calculate how far the first object travelled before the second one started.
Same time variable
Measure time from when the second object starts. Keep it consistent.
Check distances
Verify both objects have travelled the same distance at the catch-up time.
Watch Me Solve It · Consecutive numbers
+15 XP per step
Q1
PROBLEM
The sum of two consecutive even integers is 54. Find the integers.
  1. 1
    Define the variable
    Let $n$ = the first even integer.
    Consecutive even integers are 2 apart, so the next one is $n + 2$.
  2. 2
    Write the equation
    $n + (n + 2) = 54$
    The sum of the two integers equals 54.
  3. 3
    Solve and state the answer
    $2n + 2 = 54$  →  $2n = 52$  →  $n = 26$
    The integers are 26 and 28.
  4. 4
    Check the answer
    $26 + 28 = 54$  ✓  Both are even.  ✓
    The sum matches and both numbers are even. The answer is correct.
Answer26 and 28
Watch Me Solve It · Money problem
+15 XP per step
Q2
PROBLEM
Adult tickets cost $22 and child tickets cost $14. A group pays $152 for 10 tickets. How many of each type did they buy?
  1. 1
    Define variables and write two equations
    Let $a$ = adults, $c$ = children. $a + c = 10$ and $22a + 14c = 152$
    One equation for total people, one for total cost.
  2. 2
    Express one variable in terms of the other
    From $a + c = 10$:   $c = 10 - a$
    Substitute into the cost equation to get one variable.
  3. 3
    Substitute and solve
    $22a + 14(10 - a) = 152$  →  $22a + 140 - 14a = 152$  →  $8a = 12$  →  $a = 4$
    Simplify: 22a - 14a = 8a. Subtract 140: 152 - 140 = 12.
  4. 4
    Find the other value and check
    $c = 10 - 4 = 6$. Check: $4 + 6 = 10$  ✓  $22(4) + 14(6) = 88 + 84 = 152$  ✓
    Both the quantity and the cost match. The answer is correct.
Answer4 adults and 6 children
Watch Me Solve It · Catch-up problem
+15 XP per step
Q3
PROBLEM
A train leaves Sydney at 9:00 am travelling at 90 km/h. A car leaves Sydney at 10:00 am travelling at 120 km/h on the same route. When does the car catch up to the train?
  1. 1
    Calculate the head start
    In 1 hour, the train travels $90 \\times 1 = 90$ km.
    The car starts 1 hour later, so the train has a 90 km head start.
  2. 2
    Write distance equations and set them equal
    Let $t$ = hours after 10:00 am. Train distance: $90 + 90t$. Car distance: $120t$.
    At catch-up, both have travelled the same distance from Sydney.
  3. 3
    Solve for t
    $120t = 90 + 90t$  →  $30t = 90$  →  $t = 3$ hours
    Subtract 90t from both sides, then divide by 30.
  4. 4
    State the catch-up time and verify
    10:00 am + 3 hours = 1:00 pm. Train: $90 + 90(3) = 360$ km. Car: $120(3) = 360$ km.
    Both distances match. The car catches up at 1:00 pm.
Answer1:00 pm
D
Brain Trainer · Word Problems
4 problems

Four word problems covering translation, consecutive numbers, money and distance. Show each step clearly, then reveal the answer to check.

  1. 1 Five more than twice a number is 17. Find the number.

    Let $n$ be the number. Equation: $2n + 5 = 17$. Subtract 5: $2n = 12$. Divide by 2: $n = 6$. Check: $2(6) + 5 = 17$.
  2. 2 Three consecutive integers sum to 48. Find the largest integer.

    Let $n$ be the first. Equation: $n + (n+1) + (n+2) = 48$. $3n + 3 = 48$. $3n = 45$. $n = 15$. Largest: $17$. Check: $15 + 16 + 17 = 48$.
  3. 3 A taxi charges a $5 flag fall plus $2.50 per kilometre. A fare costs $32.50. How many kilometres were travelled?

    Let $d$ = distance. Equation: $5 + 2.5d = 32.5$. Subtract 5: $2.5d = 27.5$. Divide by 2.5: $d = 11$ km. Check: $5 + 2.5(11) = 32.5$.
  4. 4 A number is doubled and then 7 is subtracted. The result is 15. What is the original number?

    Let $n$ be the number. Equation: $2n - 7 = 15$. Add 7: $2n = 22$. Divide by 2: $n = 11$. Check: $2(11) - 7 = 15$.
Complete in your workbook.
+10 XP, +5 coins" data-feedback-wrong="Translate word by word. "Twice a number" = $2n$. "Five more than" = $+ 5$. "Is 17" = $= 17$. So $2n + 5 = 17$.">
1
Which equation represents "five more than twice a number is 17"?
+10 XP
2
Three consecutive integers sum to 48. What is the largest integer?
+10 XP
3
A car travels at 80 km/h for 2.5 hours. How far does it travel?
+10 XP
4
A taxi charges a $5 flag fall plus $2.50 per kilometre. A fare costs $32.50. How many kilometres were travelled?
+10 XP
5
A number is doubled and then 7 is subtracted. The result is 15. What is the original number?
+10 XP
Show Your Working
9 marks total
Apply Medium 3 MARKS

Q6. The sum of three consecutive odd integers is 81. Find the three integers. Define your variable, show all working, and check your answer.

Answer in your workbook.
Apply Medium 3 MARKS

Q7. A train leaves Sydney at 9:00 am travelling at 90 km/h. A car leaves Sydney at 10:00 am travelling at 120 km/h on the same route.

(a) How far has the train travelled by 10:00 am? (1 mark)

(b) Let $t$ be the number of hours after 10:00 am. Write an equation for when the car catches up to the train. (1 mark)

(c) At what time does the car catch up to the train? (1 mark)

Answer in your workbook.
Evaluate Medium 3 MARKS

Q8. A school fundraiser sells chocolate bars for $3 each and cookies for $2 each. They sell 150 items in total and raise $380.

(a) Define variables and write two equations. (1 mark)

(b) Solve to find how many chocolate bars and how many cookies were sold. (1 mark)

(c) Verify your answer by checking both the total number of items and the total money raised. (1 mark)

Answer in your workbook.
Comprehensive Answers

Quick Check

1. B -- "Twice a number" = $2n$, "five more than" = $+ 5$, "is 17" = $= 17$.

2. B -- $n + (n+1) + (n+2) = 48$ → $3n + 3 = 48$ → $n = 15$. Largest = 17.

3. C -- $d = rt = 80 \times 2.5 = 200$ km.

4. B -- $5 + 2.5d = 32.5$ → $2.5d = 27.5$ → $d = 11$ km.

5. C -- $2n - 7 = 15$ → $2n = 22$ → $n = 11$.

Show Your Working Model Answers

Q6 (3 marks): Let $n$ = first odd integer [0.5]. $n + (n+2) + (n+4) = 81$ [0.5]. $3n + 6 = 81$ [0.5]. $3n = 75$ → $n = 25$ [0.5]. The integers are 25, 27, and 29 [0.5]. Check: $25 + 27 + 29 = 81$ ✓ [0.5].

Q7 (3 marks): (a) By 10:00 am, the train has travelled $90 \times 1 = 90$ km [1]. (b) Distance of train after $t$ hours: $90 + 90t$. Distance of car: $120t$. Equation: $120t = 90 + 90t$ [1]. (c) $30t = 90$ → $t = 3$ hours. The car catches up at 1:00 pm [1].

Q8 (3 marks): (a) Let $c$ = chocolate bars, $k$ = cookies. $c + k = 150$ and $3c + 2k = 380$ [1]. (b) From first equation: $k = 150 - c$. Substitute: $3c + 2(150 - c) = 380$ → $c = 80$, $k = 70$ [1]. (c) Check items: $80 + 70 = 150$ ✓. Check money: $3(80) + 2(70) = 240 + 140 = 380$ ✓ [1].

Stretch Challenge · +25 XP, +10 coins

The Pool Puzzle

A swimming pool has two pipes. Pipe A fills the pool in 6 hours. Pipe B empties the pool in 8 hours. The pool is initially empty. If both pipes are turned on at the same time, how long will it take to fill the pool? Hint: think about the fraction of the pool each pipe handles in one hour.

Reveal solution

Pipe A fills $\frac{1}{6}$ of the pool per hour.

Pipe B empties $\frac{1}{8}$ of the pool per hour.

Combined rate: $\frac{1}{6} - \frac{1}{8} = \frac{4}{24} - \frac{3}{24} = \frac{1}{24}$ of the pool per hour.

Time to fill: $\frac{1}{\frac{1}{24}} = 24$ hours.

It takes 24 hours to fill the pool with both pipes running.

R
Quick Review

Read Twice

Understand before you calculate

Define Clearly

Write "Let n = ..." in full sentences

One Variable

Express all unknowns in terms of a single letter

Two Equations

Quantity and cost for money problems

Distance = Rate x Time

The foundation of all motion problems

Check with Words

Plug back into the original sentence

Interactive: Problem Solver

Practise translating word problems into equations with scaffolded hints and instant feedback.

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