This year Jerry is half as old as his dad and 1/3 the age of his grandfather. If the sum of their ages is 132, how old is Jerry?
J is age of Jerry.
D is age of Dad
G is age of grandfather.
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You know 2J = Dad's age
You know 3J = Granfathers age
You know D + J + G = 132.
For D substitute 2J
For J you have J
For G substitute 3J
2J + 3J + J = 132
Solve for Jerry's age.