Science Kit M and Science Kit N had the same usual price. During a sale, Kit M was sold at 30% off its usual price and Kit N was sold at $36 off its usual price. Wei Jie wanted to buy a kit during the sale. He could not buy Kit N as he was short of $14.50, so he bought Kit M and had $21.50 left.
- What was the usual price of each kit?
- How much money did Wei Jie have at first?
Need a hint?
Find how much more Kit N costs than Kit M in the sale. Use the money he was short and the money he had left.
Worked answer
- (a) Kit N costs more than Kit M by the money he was short plus the money he had left: $14.50 + $21.50 = $36.
- Kit M costs 70% of the usual price. Kit N costs the usual price take away $36.
- So the usual price − $36 is $36 more than 70% of the usual price.
- The usual price − 70% of the usual price = 30% of the usual price.
- 30% of the usual price = $36 + $36 = $72.
- 10% of the usual price = $72 ÷ 3 = $24, so the usual price = $24 × 10 = $240.
- (b) Kit M costs 70% of $240 = 7 × $24 = $168.
- Money at first = $168 + $21.50 = $189.50.
Answer: $189.50
The mistake this question tests
Habit
Percentage of a new total
Many pupils think the usual price is found by 36 ÷ 30%, forgetting that Kit N's $36 discount is also taken off. The 30% discount must be compared with the $36 discount first.
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