Using the fact that 1/3rd of the fruit in bag 1 are apples and there are 20 apples in total you can work out that there are 60 pieces of fruit in bag 1. This is found by doing 20 x 3 = 60.
Then using the fact that both bags have an equal number of fruit in total, you can find that the solution to the problem will be 15% of 60. This can be found by working out 10% of 60 which is 6 and then finding 5% of 60 which is 3 (this can be done by halving 6). 10% and 5% are then added to find 15% of 60 which is 9. This is the solution.