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.

J = M + 2
M - 2J = 0
J + M = 21
J - 2M = 0

Respuesta :

Answer:

Mary is 7

Because 14+7 =21

So j+m=21

J - 2m= 0