Solving a problem with a fraction

Question

At a school fair, 3/10 of the pies sold had cheese filing, 1/4 had beef filing and the remaining 90 pies had potato filing. what fraction of the pies had potato filing? how may pies were sold at the fair

Answer 1

3/10 + 1/4 = 6/20 + 5/20 = 11/20

1 - 11/20 = 9/20 = 90/total pies

90/T = 9/20

10/T = 1/20

T=200 pies total sold

60 cheese pies sold

50 beef pies sold

90 potatoes sold

sum to 200 pies total

60+50+90 = 200