SOLUTION: Ricardo is 4 years less than twice as old as his sister. The sum of their ages is 20. How old is Ricardo?

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Question 72517: Ricardo is 4 years less than twice as old as his sister. The sum of their ages is 20. How old is Ricardo?
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
Let r=ricardo's age, s=sister's age
2s-4=r Here's their age relationship
s%2Br=20Sum of their ages
s=20-rSolve for s
2%2820-r%29-4=rPlug in s=20-r
40-2r-4=rsolve for r
36=3r
36%2F3=r
r=12
So ricardo is 12 and his sister is:
s=20-12
s=8
Check:
2%288%29-4=12
16-4=12
12=12Works