Question

Mark’s father is 55. This is 15 years older than twice Mark's age. How old is Mark? Explain the method used for solving the problem. Include a restatement of the problem, the steps you used to solve the problem, the answer, and an explanation of how you know the answer is correct.

Answer 1

Mark's father is 55.  f=55

And this is equal to twice Mark's age plus 15, f=2m+15

Since f=f we can say

2m+15=55  subtract 15 from both sides

2m=40  divide both sides by 2

m=20

So mark is twenty years old.

We can check...

2m+15=55, since m=20 this becomes

2(20)+15=55

40+15=55

55=55

Answer 2

Mark is 20. 55 - 15 = 40, 40 / 2 = 20. Mark is 20