Hey! What is the best way to answer this type of question? Is there any trick or shortcut?
The question is from the BMAT 2020 (Q25)
Thank you so much in advance! 
Hey!
the 50p coin cannot be used. The total value of the remaining 21 coins is 73p, so the coins that I don’t use will have a value of 24p. The most efficient way to make 24p will use 4 coins (two 10p coins and two 2p coins), so 17 is the maximum number of coins that can be used to pay the exact price, which is option D.