SOLUTION: How old is the younger of two siblings if the sum of their ages is 18 and the difference is 10?

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Question 689894: How old is the younger of two siblings if the sum of their ages is 18 and the difference is 10?
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

let's the younger of two siblings be x (the older of two siblings) and y (the younger of two siblings)

if the sum of their ages is 18, we have
x%2By=18.........eq. 1

and if the difference is 10, we have
x-y=10.........eq. 2

solve the system:

x%2By=18.........eq. 1
x-y=10.........eq. 2
________________________

x%2By=18.........eq. 1.....solve for x

so, the younger of two siblings is 4 years old

x=18-y..........eq. 1a..........plug it in eq. 2

x-y=10.........eq. 2
18-y-y=10
18-2y=10
18-10=2y
8=2y
8%2F2=y
highlight%28y=4%29
now go to eq. 1a and find x

x=18-y..........eq. 1a
x=18-4
highlight%28x=14%29
so, the younger of two siblings is 4 years old