Question

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

b,c ?

Answer 1

....its multiple choice

Answer 2

c is right

Answer 3

what else??

Answer 4

i dont know i was just wondering which ones are correct......so just c

Answer 5

Also a

Answer 6

no

Answer 7

no a is correct also J = 2M
then subtract 2M from both sides

Answer 8

From the problem we know:
X) J = 2*M
Y) J + M = 21

Substituting 2*M into Y
Y) 2*M + M =21
M = 7
J = 14

So these equations are correct
a) J - 2M = 0
c) J + M = 21

Answer 9

thanks guuys

Answer 10

good job!!!

Answer 11

u r welcome