
Hyunjeong O. answered 05/01/19
Friendly and Experienced ACT Math Tutor!
Let's set equation using variables.
x = number of pens he bought
y = number of pencils he bought
Total 300 pens and pencils -> x + y = 300
Total costs -> 0.25*x + 0.15*y = 62.50
We need to find the value of "x", so lets substitute y with x to make equation with only one variable x.
y = 300 - x
0.25*x + 0.15*(300-x) = 62.50
0.25x + 45 - 0.15x = 62.50
0.1x = 17.5
x = 175
Answer : 175 pens
Hope this is helpful ! :)