Question

Mark is y years old. In five years' time, Jack will be twice as old as Mark and Daniel will be 2 years younger than Jack is now. Write an expression in y for the sum of their 3 ages now.

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Answer 1

5y + 3 is the sum of the three ages

Explanation:

Let y=Mark, d=Daniel j=Jack, and s=The sum

Mark is y years old. In five years jack will be twice as old as Mark

j + 5 = 2(y+5)

j + 5 = 2y + 10

j = 2y + 10 - 5

j = 2y + 5

Daniel will be two years younger than jack is now

d + 5 = j - 2

d = j - 2 - 5

d = j - 7

Replace j with (2y+5)

d = (2y+5) - 7

d = 2y - 2

Expression in terms of y for the sum of the 3 ages now

s = y + j + d

replace j and d with expressions we came up with above

s = y + (2y+5) + (2y-2)

s = y + 4y + 3

s = 5y + 3 is the sum of the three ages