The ratio of blue to purple stamps Eva had was 5:2. The cost of each of the blue stamps was $1 and the cost of each of the purple stamps was $2. Eva sold 40% of the blue stamps and the total cost of the unsold stamps was $455. How many blue stamps did she have left?

Answer 1

number of blue stamps ---- 5x
number of purple stamps ---- 2x

value of blue stamps = 5x dollars
value of purple stamps = 4x dollars
total cost of all stamps = 9x dollars

she sold 4% of blue stamps, so 60% are left
which means number of blue stamps left = .6(5x) = 3x stamps are left
value of stamps left :
1(3x) + 4x = 455
7x = 455
x = 65

All can now be found, continue .....