Question 1036236
A father and his son have a combined age of 145.
f + s = 145
s = -f + 145
 When the father was his son's current age he was twice as old as his son.
let d = f - s; (the difference in their ages)
f - d = 2(s - d)
f - d = 2s - 2d
f = 2s - 2d + d
f = 2s - d
replace d with (f-s)
f = 2s -(f-s)
f = 2s - f + s
f + f = 2s + s
2f = 3s
replace s with (-f+145)
2f = 3(-f+145)
2f = -3f + 435
2f + 3f = 435
5f = 435
f = 435/5
f = 87 yrs is father's present age
then
s = 145 - 87
s = 58 yrs is the son's 
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Check this in the statement (87-58 = 29 yrs is the difference their ages)
"When the father was his son's current age he was twice as old as his son.
87 - 29 = 2(58-29)
58 = 2(29)