SOLUTION: Ruby is 5 years older than Paula. She is also 7 years older than Shelly. The sum of their ages is 21. How old is each person? Justify your answer.

Question 936779: Ruby is 5 years older than Paula. She is also 7 years older than Shelly. The sum of their ages is 21. How old is each person? Justify your answer.
Found 3 solutions by TimothyLamb, Edwin McCravy, 428225:
Answer by TimothyLamb(4379)   (Show Source): You can put this solution on YOUR website!
x = ruby age now
y = paula age now
z = shelly age now
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x = y + 5
x = z + 7
x + y + z = 21
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put the system of linear equations into standard form
---
x - y = 5
x - z = 7
x + y + z = 21
---
copy and paste the above standard form linear equations in to this solver:
https://sooeet.com/math/system-of-linear-equations-solver.php
---
solution:
x = ruby age now = 11
y = paula age now = 6
z = shelly age now = 4
---
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Answer by Edwin McCravy(20056)   (Show Source): You can put this solution on YOUR website!

Substitute (P+5) for R in the 2nd and 3rd.
Solve the 2nd for S
Substitute that for S in the 3rd
Substitute back to find P and R.
Solutions: P=6, R=11, S=4
Edwin
Answer by 428225(90)   (Show Source): You can put this solution on YOUR website!
Let x be the unknown age of Shelly
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x+x+2+x+7=21
3x+9=21(subtract 9)
3x=12 (divide by 3)
x=4
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Therefore Shelly is 4 years old.
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Since Shelly is 7 years younger than Ruby and Paula is only 5 years younger than Ruby; Paula is 2 years older than Shelly.
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Therefore Paula is 6
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Since Ruby is 7 years older than Shelly, Ruby must be 11.
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