SOLUTION: please help me to solve this equation.In 3 years ,Alex will be 3 times as old as his sister Percy.A year ago,Alex was 7 times as old as Percy.How old are they now?

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: please help me to solve this equation.In 3 years ,Alex will be 3 times as old as his sister Percy.A year ago,Alex was 7 times as old as Percy.How old are they now?       Log On


   

Question 148582: please help me to solve this equation.In 3 years ,Alex will be 3 times as old as his sister Percy.A year ago,Alex was 7 times as old as Percy.How old are they now?
Answer by vleith(2983) About Me  (Show Source):
You can put this solution on YOUR website!
Let Alex's age now be a. Let Percy's age be p
In three years, Alex will be a+3 and Percy will be p+3
Last year, Alex was a-1 and Percy was p-1
You are told that in 3 years Alex will be 3 times as old as Percy
a%2B3+=+3%28p%2B3%29
a%2B3+=+3p+%2B+9
a+-+3p+=+6
You are also told that last year Alex was 7 times older than Percy
a-1+=+7%28p-1%29
a-1+=+7p+-+7
a+-+7p+=+-6
Now you can use substitution or elimination to solve. We'll use elimination here
a+-+3p+=+6
a+-+7p+=+-6 Subtract the second equation from the first -a%2B7p+=+6
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0a+%2B+4p+=+12
4p+=+12
p+=+3
Percy is 3 now.
So that makes Alex a+-+3p+=+6
a+-+3%2A4+=+6
a+-+9+=+6+
a+=+15
Alex is 15.
Check your answers.
is 15-1 = 7*2 check
is 15+3 = 3(3+3) check