Becca’s age is 3 less than one half of Faith’s age. The total is 21, what’s are the sisters’ ages?

Question

Becca’a age a 3 less than ½ of Faith’s age. The total number is 21, what would be Becca and Faith’s ages?

Answer 1

Let B = Becca's age and F = Faith's  age.

B + F = 21

B = F/2 - 3

 

This system can be solved in several ways; here is one.

 

Substitute the second equation into the first.

F/2 -3 + F = 21

Collect terms and add 3 to each side => (3/2)F = 24

Multiply by 2/3: F = 16 

Substitute in either equation to get B = 5