maths
posted by jess .
john has a total of 9 stamps, which consists of 25cent and 2cent stamps. his stamps have a value of $1.10. how many of each stamp does john have?

To get an even amount ($1.10), you need either two quarter stamps ($.50) or four quarter stamps ($1.00) with the remainder in $.02 stamps. Which would involve 9 stamps?
I hope this helps. Thanks for asking. 
4 x 25 stamps and 5 x .02 = 1.10

but how..... i can't understand it!