A public telephone has been vandalised and will take only 50 pence coins and 10 pence coins. A
woman puts £8.50 into the phone to make a long-distance call with twenty-five coins. Five 10
pence coins are returned when she finishes her call.
What combination of coins is retained by the machine?
A Twice as many 10s as 50s.
B One-and-a-half times as many 50s as 10s.
C The same number of 50s and 10s.
D Three times as many 50s as 10s.
E One-and-a-half times as many 10s as 50s.
The answer is D but why?? Thank you for your help!