# algebra

Classes A and B have 35 students each. If seven girls shift from class A to class B, then the number of girls in the classes would interchange. If four girls shift from class B to class A, then the number of girls in class A would be twice the original number of girls in class B. What is the number of boys in class A and class B?

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1. I am assuming that the 2nd shift follows the first shift

now:
let the number of girls in A be x
let the number of girls in B be y

after 1st shift:
A has x-7
B has y+7
"the number of girls in the classes would interchange"
---> y+7 = x

2nd shift
A has x-7 + 4 = x-3
B has y+7 - 4 = y-3
" the number of girls in class A would be twice the original number of girls in class B"
--> x-3 = 2y or x = 2y+3

so 2y+3 = y+7
y = 4
x = 11

so originally, there were 24 boys in A and 31 in B

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posted by Reiny

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