I was informed maths books do have errors in, which is crazy because it defeats the whole object of testing yourself from a book if it gives incorrect answers

Q: A gym subscription is either £500 per year, or £50 per month over twelve months. It would be cheaper to borrow £500 from a bank for twelve months at an APR of 20% and pay the gym in full rather than to pay monthly.

TRUE / FALSE / CANNOT SAY

So i calculate £500 borrowed at 20% APR = £600. £50 per month for year = £600. So the answer is FALSE.

But no, the answer is:

A: True (the total payable on a £500 loan at an APR OF 20% would be £550 as the interest is constantly reducing as the loan is repaid. Paying £50 pound for twelve months totals £600 and so is more expensive).

- the question says nothing about the loan being repaid so how am i supposed to know or even guess this.