What is the least number of coins needed to make 42p?

To make 42p using the least number of coins, you can use the following combination: 1 twenty pence coin, 1 ten pence coin, and 2 one pence coins. This totals 4 coins: 20p + 10p + 1p + 1p = 42p. Thus, the least number of coins needed is 4.