Question

POIN 100 lhooo......... TWO years ago. the sum of the ages of a boy and his younger sister was 20 years. THREE years from now. their ages wikl differ by 10 years. From a pair of simultaneous equations and find their present ages??

Answer 1

For example: boy's age = x and his sister = y, so

(x - 2) + (y - 2) = 20
x - 2 + y - 2 = 20
x + y - 4 = 20
x + y = 20 + 4
x + y = 24 ... first equation

(x + 3) - (y + 3) = 10
x + 3 - y - 3 = 10
x - y = 10 ... second equation

now eleminate them

x + y = 24
x - y = 10 +
2x = 34
x = 17

then, substitute
x + y = 24
17 + y = 24
y = 24 - 17
y = 7

so, present the boy is 17th and his sister is 7 years old

hopefully help you :)