SOLUTION: Susan is 10 years old then her brother . In three years time,she will be twiced as old as her brother. What are their present ages?

Question 970972: Susan is 10 years old then her brother . In three years time,she will be twiced as old as her brother. What are their present ages?
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
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)

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