Alfie buys two books, each at the same price. he pays with a £10 note and gets £2.30 change.
what is cost of one book?

First subtract the amount he paid from the amount of change he got:

10 - 2.30 = 7.70

So the price for the two books was £7.70, now divide by 2.

7.70 / 2 = 3.85

So each book cost £3.85