Question

A girl is twice as old as her sister. four years hence, the product of their ages will be 160 find the present ages?

Answer 1

Let the girl be 'x' . And Let her sister be '2x'.

Therefore,

(2x+4)(x+4)=160

2x^2+8x+4x+16=160

2x^2+12x=160-16

2x^2+12x=144

2(x^2+6x)=144

X^2+6x=72

X^2+6x-72=0

X^2+12x-6x-72=0

X(x+12)-6(x+12)=0

(X-6)(x+12)

X=6

Or x=-12

Since age cannot be negative .

Therefore,

the girls present age is 6yrs and

Her sister's age is 12yrs.

Answer 2

he girls present age is 6yrs and  

Her sister's age is 12yrs.