Brian's age is 9 less than 5 times Stewie's age. The sum of their ages is 9. Find their ages.

Answer 1

Lets us assign variables for the unknowns;

S : Stewie

B : Brian

Keywords are: 9 less than (means that subtract 9 years from Brian)

5 times Stewie's age (means 5 * S)

sum (means add)

Use this information to write an equation

B = 5*S - 9 --> 1st equation

B + S = 9 --> 2nd equation

substitute B in the first equation with the second one

B + S = 9 --> (5*S - 9) + S = 9

5S - 9 + S = 9

5S + S - 9 = 9 --> combine like times

6S - 9 = 9 --> inverse operation

+9 +9

6S = 18 (divide 6 from both sides)

S = 3 --> Stewie's age is 3 years

Use this to find Brian's age

B = 5*S - 9 --> 1st equation

B = 5*3 - 9

B = 6 --> Brian's age is 6 years

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