Katie is twice as old as her sister Mara. The sum of their ages is 24. Find their ages.

So k=katie's' age

m=mara's age

k is 2 times as old as m

k=2m

sum is 24

add means sum

k+m=24

so we have

k+m=24 and

k=2m

subsitute

2m+m=24

add

3m=24

divide both sides by 3

m=8

subsitute again

k=2m

k=2 (8)

k=16

katie=16

mara=8