Donald's Donuts
Donald Donuts is having a sale on donuts. For every 5 donuts that you buy, you get 1 free. If Mickey wants to have 200 donuts for a party, how many must he buy?
Details and assumptions
Note: If Micky buys 1000 donuts, he only gets 200 free donuts. He does not get another 40 free donuts because of the 200 free donuts.
The answer is 167.
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1 solution
Solution 1: If Mickey bought 165 donuts, he will get 5 1 6 5 = 3 3 free, for a total of 198. Hence, he must buy 167, along with the 33 free, to get a total of 200.
Solution 2: If Mickey received 20% of each donut extra, he will get 120% of what he purchased. Observe that 1 2 0 % 2 0 0 × 1 0 0 % ≈ 1 6 6 3 2 , which would make a good place to start guessing. We check that with 167 donuts, he will receive 33 free donuts, making a total of 200.