How Old Is John?
Joe is 4 years older than John. Sam is twice as old as Joe. The sum of their age is 68.
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Write out the equations as you read them;
Joe = John + 4
Sam = 2 x Joe
Joe + John + Sam = 68
You have 3 equations and 3 unknowns. If they are independent equations, you can find a solution.
Substitute
2 x (John + 4) for Sam
and John + 4 for Joe
(John + 4) + (John) + 2(John + 4) = 68
Now you have one equation and one unknown. Solve for John;
John + 4 + John + 2John + 8 = 68
4John = 56
John = 56/4 = 14
Now we can calculate the rest;
Joe = John + 4 = 14 + 4 = 18
Sam = 2(Joe) = 2(18) = 36
Now, don't assume it's correct until we check everything;
Joe + John + Sam = 18 + 14 + 36 = 68
yes, it checks, so there you go.
Joe = John + 4
Sam = 2 x Joe
Joe + John + Sam = 68
You have 3 equations and 3 unknowns. If they are independent equations, you can find a solution.
Substitute
2 x (John + 4) for Sam
and John + 4 for Joe
(John + 4) + (John) + 2(John + 4) = 68
Now you have one equation and one unknown. Solve for John;
John + 4 + John + 2John + 8 = 68
4John = 56
John = 56/4 = 14
Now we can calculate the rest;
Joe = John + 4 = 14 + 4 = 18
Sam = 2(Joe) = 2(18) = 36
Now, don't assume it's correct until we check everything;
Joe + John + Sam = 18 + 14 + 36 = 68
yes, it checks, so there you go.
1
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Thank you for your answer. Although it is lengthier than I had thought. Is there any other way to answer this problem?
Nice explanation my friend! I'll give ya a wow!...♥nassy
I just wanted you to see the steps. Yes, there are shorter ways to solve simultaneous equations, but leave that for college.
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