Question 1024911
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Carol is three times as old as John who is ten years older than Henry. The sum of their ages is 140 years. Calculate their ages. 
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C = 3J,           (1)     ("Carol is three times as old as John")
J = H + 10,       (2)     ("John . . . is ten years older than Henry")
C + J + H = 140.  (3)     ("The sum of their ages is 140 years")


Substitute (1) and (2) into (3). You will get

3J + (H + 10) + H = 140.   (4)

Substitute (2) into (4). You will get a single equation for H:

3*(H+10) + (H+10) + H = 140.

Simplify and solve it for H:

3H + 30 + H + 10 + H = 40,
5H = 140 - 30 - 10 = 100,

H = {{{100/5}}} = 20.  It is Henry's age.

Then John is J = H + 10 = 20 + 10 = 30 years,  and
C = 3J = 3*30 = 90 years for Carol.
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