Question 728206
Mr. Klinker is 35 and his daughter is 10.  In how many years will Mr. Klinker be twice as old as his daughter?

What mathematical concept is this and how do you set it up, please?
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The difference in age is, and always will be, 25 years.
If he's 2x her age, --> 50 & 25.
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The hard way:
k = his age
d = her age
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35 + x = (10 + x)*2
35 + x = 20 + 2x
x = 15
--> in 15 years
same answer