SOLUTION: jerry was 1/3 as young as his grandpa 15 years ago. if the sum of their ages is 110, how old is his granpa?

Question 320714: jerry was 1/3 as young as his grandpa 15 years ago. if the sum of their ages is 110, how old is his granpa?
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
Here is a simple step-by-step method that you can apply to most of these age problems.
:
Let g = grandpa's present age
Let j = Jerry's present age
:
Write an equation for each statement, simplify the equations:
:
"jerry was 1/3 as young as his grandpa 15 years ago."
j - 15 = (g - 15)
Multiply both sides by 3
3(j-15) = g - 15
3j - 45 = g - 15
3j = g - 15 + 45
3j = g + 30
:
"if the sum of their ages is 110,"
j + g = 110
j = (110-g)
:
how old is his granpa?
Substitute (110-g) for j in the 1st equation; 3j = g + 30:
3(110-g) = g + 30
330 - 3g = g + 30
330 - 30 = g + 3g
300 = 4g
g =
g = 75 yrs old is Grandpa
:
:
Confirm that this is true, find Jerry's age
j = 110 - 75
j = 35 yrs is Jerry's age
Check these values in the statement:
"jerry was 1/3 as young as his grandpa 15 years ago."
35 - 15 = (75 - 15)
20 = (60)
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