Problem 21 · 2014 Math Kangaroo
Stretch
Arithmetic & Operations
work-backward
Heinzi the kangaroo has bought some toys. For them he gave 150 kangoo-coins (KC) and received 20 kangoo-coins back. Just before leaving the shop he changed his mind and exchanged one of the toys he had bought for another one. Because of this he received a further 5 kangoo-coins back from the shopkeeper. Which of the toys in the picture has Heinzi taken home with him? (The price of each toy is shown on its tag.)
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Answer: A — Carriage and Aeroplane
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Hint 1 of 3
Work out how many coins Heinzi really spent in the end, after all the change he got back.
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Hint 2 of 3
He handed over 150, then got 20 back, then 5 more back, so take both amounts away.
Still stuck? Show hint 3 →
Hint 3 of 3
Now look at the price tags and find the toys that add up to exactly that many coins.
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Approach: net spending, then match a price pair
- He paid 150 and got 20 back, then 5 more back after the exchange: net 150 − 20 − 5 = 125.
- The toys he kept must cost 125 together.
- Carriage (73) + Aeroplane (52) = 125; no other pair fits.
- Answer: Carriage and Aeroplane.
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