Question 970972
 Susan is 10 years older than her brother.
 In three years time, she will be twice as old as her brother.
 What are their present ages?
:
let s = Susan's age
let b = brother's age
:
Write an equation for each statement
" Susan is 10 years older than her brother"
s = b + 10
:
In three years time, she will be twice as old as her brother."
s + 3 = 2(b + 3)
s + 3 = 2b + 6
s = 2b + 6 - 3
s = 2b + 3
replace s with (b+10) from the 1st statement.
b + 10 = 2b + 3
10 - 3 = 2b - b
7 = b
Brother is 7 yrs old
then
7 + 10 = 17 yrs is Susan's age
:
:
Check these solutions in the statement
In three years time, she will be twice as old as her brother."
17 + 3 = 2(7 + 3)
20 = 2(10)