No because....
A childs toy consisting of a hand held game and a battery costs £21. The Game costs £20 more than the battery, how much does the battery cost?
Right??

So if the above quote was correct then, because the toy costs 20pound more than the battery, then the the toy alone would cost 21pound making a total of 22pounds for the toy and batt!(because you are saying the batt is 1pound).

It says the TOTAL cost of the batt and toy costs 21pound therefore the batt must cost 50p.
20pound more than 50p is 20.50 yes?
So 20.50 + 50p =21pounds

Or have i confused it further