Question

One day at St. Philip's High School, 1/2 of the pupils walked to school, 1/5 of the pupils came to school by bus, and the remaining 57 pupils came by car. so then How many pupils are there in the school?

Answer 1

Let P be the number of kids,
we know P>57
take 1-(1/2)-(1/5)=3/10
therefore 57 is 3/10P
3/7P=57
P=57*7/3=133 is the answer
it would be incorrect if we didnt get a positive integer.