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john is now three times as old as his brother Sam. In five years, john will be twice as old as Sam will be then. Find their present ages.



Answer :

apologiabiology
j=john's age now
s=sam's age now

j=3 times s
j=3s
in five years (j+5,s+5)
j+5=2 times (5+s)
j+5=2(s+5)
j+5=2s+10
subtract 5 from both sides
j=2s+5
use other equation
j=3s
j=2s+5
subsitute
3s=2s+5
subtract 2s
s=5

sam=5
j=3s
j=3 times 5
j=15


john=15
sam=5

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