Hn 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 syst
em equations that represents the problem.
2 answers:
System of equations:
J =2M
J+M=21
2M+M=21
3M=21
M=7
Equation:
M + 2M = 21
Explanation:
M = Mary's age.
2M = Jhon's age is double Mary's age (2 times)
M + 2M = The sum of these two needs to be 21.
Solving the equation:
M + 2M = 21
3M = 21
M = 21 / 3
M = 7
Mary's age is: 7
Jhon's age is two times Mary's: 7 + 7 = 14
Proof : 7 + 14 = 21
Hope it helped,
Happy homework/ study/ exam!
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