Step-by-step explanation:
the Bank of England issues coins with values of 1, 2, 5, 10, 20, and 50 pence.
so, we could actually use only 2 coins for 70 pence (1×50 + 1×20).
but, since we have to use 4 coins, it has to be
3×20 + 1×10 (3 times 20 pence and 1 time 10 pence)
