Question 1018389
let m = the 1st guy
let y = the other guy
let d = (m - y), the difference in their ages
:
 I'm thrice as old as you were, when I was as old as you are.
m = 3(y - d)
Replace d with (m-y)
m = 3(y - (m-y))
remove brackets
m = 3(y - m + y)
m = 3(2y - m)
m = 6y - 3m
m + 3m = 6y
4m = 6y
Simplify, divide by 2
2m = 3y
:
 Our current ages add up to 80. How old are you and me ?
m + y = 80
y = -m + 80
replace y in the equation 2m = 3y, with (-m+80)
2m = 3(-m+80)
2m = -3m + 240
2m + 3m = 240
5m = 240
m = 240/5
m = 48 yrs is the 1st guys age
Find y
y = -48 + 80
y = 32 yrs is the 2nd guys age
:
:
Check this: 48 - 32 = 16 is the difference in their ages
"I'm thrice as old as you were, when I was as old as you are."
16 yrs ago the 1st guy was 32, the 2nd guy was 16
48 = 3(32 - 16)