Janitor spray bottle

Question

A janitor had 2/5 of a spray bottle of cleaning solution, he used 1/8 of it in a day, how much cleaning solution is left?

Answer 1

2/5 - 1/8

change the two fractions so they have the same denominator 5x8= 40

= 2(8)/5(8) - 1(5)/8(5)

= 16/40 - 5/40

then add or subtract the numerators

= (16-5)/40

= 11/40 left

or

2/5 = .4

1/8 = .125

.4-.125 = .275

.275 = 11/40