Question 989927
.
J=john's age; A=Jake's age=J+5; I=Jill's age=2J; 
N=Jan's age=J-5
.
J+A+I+N=75
J+(J+5)+(2J)+(J-5)=75
5J=75
J=15
ANSWER 1: John is 15 years old.
A=J+5=15+5=20
ANSWER 2: Jake is 20 years old.
I=2J=2(15)=30
ANSWER 3: Jill is 30 years old.
N=J-5=15-5=10
ANSWER 4: Jan is 10 years old.