Question

There are two buildings P and Q. If
15 persons are sent from P to Q, then the
number of per sons in each building is
the same. If 20 persons are sent from Q
to P, then the number of persons in P
is double the number of persons in Q.
How many persons are there in
building P?​

Answer 1

p-15=x

Q+15=x

We put the value of x in equation 1

p-15=Q+15

p=Q+30(a)

p+20=2Q

we put the value of p from eq a

Q+30+20=2Q

Q=25

P=30