Answer:
Subtract the amount of £1 coins from 50p coins:
256-172 = 84
84/3 coins = 28 people paid with 3 coins.
172 people paid using £1 coins
172 + 28 = 200 total people
percent who used 3 coins = 28/200 = 0.13 x 100 = 14% so the answer is 14%
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