SOLUTION: The sun of Anna's age and Ben's age is 40.Two years ago, Anna was thrice as Ben. Find the Anna's age

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Question 1199605: The sun of Anna's age and Ben's age is 40.Two years ago, Anna was thrice as Ben. Find the Anna's age
Found 3 solutions by math_tutor2020, josgarithmetic, greenestamps:
Answer by math_tutor2020(3817)   (Show Source): You can put this solution on YOUR website!

A = Anna's current age
B = Ben's current age

The sum of these current ages is 40.
A+B = 40
Pick A or B to isolate. I'll solve for B.
B = 40-A


A-2 = Anna's age two years ago
B-2 = Ben's age two years ago

Two years ago, Anna was thrice as Ben.
A-2 = 3(B-2)

Apply substitution and solve for "A".
A-2 = 3(B-2)
A-2 = 3(40-A-2) ...... replace B with 40-A
A-2 = 3(38-A)
A-2 = 114-3A
A+3A = 114+2
4A = 116
A = 116/4
A = 29
Anna is currently 29 years old.

B = 40-A
B = 40-29
B = 11
Ben is currently 11 years old.

Rewind the clock 2 years.
Anna was 29-2 = 27 years old.
Ben was 11-2 = 9 years old.
We see that Anna's past age is exactly triple that of Ben's past age (3*9 = 27).
The answer is confirmed.

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Answer: Anna's current age is 29 years old

Answer by josgarithmetic(39620)   (Show Source): You can put this solution on YOUR website!
x, Anna
y, Ben


Question asks for x.


-





Answer by greenestamps(13200)   (Show Source): You can put this solution on YOUR website!


You have received two responses, both showing a typical solution using two variables, and setting up the problem using the information exactly as given.

Both solution methods are fine; however, the amount of work required to reach the final answer can be a lot less if you take the time to analyze the given information and set up the problem for solving using a single variable.

Here is how I would set up and solve the problem.
let x = Ben's age 2 years ago
then 3x = Anna's age 2 years ago

The sum of their ages now is 40:

(x+2)+(3x+2) = 40
4x+4 = 40
4x = 36
x = 9

ANSWER: Anna's age is 3x+2 = 29


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