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13-07-2016
Mathematics

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john is twice as old as mary. the sum of their ages is 21. how old is mary? let j = john's age and m = mary's age. select the system equations that represents the problem.

Respuesta :

13-07-2016

Hello,

let's assume j the john's age, m the mary's age.

"John is twice as old as mary"==>j=2*m

"the sum of their ages is 21" ==>j+m=21

==>2*m+m=21
==>3m=21
==>m=7
and j=21-7=14

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