Mathematical Reasoning
The ratio of Adam's savings to John's savings was 9 : 4. After Adam spent \$63, the ratio became 3 : 2. How m…
Question 1 · Multiple choice
Question
The ratio of Adam's savings to John's savings was 9 : 4. After Adam spent $63, the ratio became 3 : 2. How much savings did John have?
Options
- A.$56
- B.$63
- C.$72
- D.$84
- E.$126
Correct answer
Explanation
Step 1: Express both savings using one variable
Original ratio Adam : John = 9 : 4.
Let Adam's savings = 9k and John's savings = 4k.
Step 2: Set up the equation for the new ratio
John's savings are unchanged (he doesn't spend anything).
After Adam spends $63:
- Adam has: 9k − 63
- John still has: 4k
The new ratio is 3 : 2:
(9k − 63) : 4k = 3 : 2
Step 3: Solve for k
Cross-multiply (means × extremes):
2 × (9k − 63) = 3 × 4k
18k − 126 = 12k
18k − 12k = 126
6k = 126
k = 126 ÷ 6 = 21
Step 4: Find John's savings
John = 4k = 4 × 21 = $84
Check:
- Adam originally: 9 × 21 = $189
- After spending: $189 − $63 = $126
- New ratio: $126 : $84 = 3 : 2 ✓
Answer: John has $84
| Option | Value | Why it is wrong |
|---|---|---|
| A | $56 | Used k = 14 — solved the equation incorrectly. ✗ |
| B | $63 | Confused Adam's spend with John's savings. ✗ |
| C | $72 | Used k = 18 — arithmetic slip. ✗ |
| D | $84 | 4 × 21 = 84. ✓ |
| E | $126 | Found 6k = 126 but gave that as the answer instead of 4k. ✗ |