Question

A girl is twice as old as her sister. Five years hence, the product of thier ages ( in years ) will be 375. Find their present ages..

Answer 1

Given :

• A gírl is twice as old as her sister
• Five years hence, the product of their agës ( in years ) will be 375.

To Find :

• Present gírl age
• Present of her sister's age

Solution :

Let the age of the girl be = 2y years.

Her sister's age is = y years

( 2y + 5 ) ( y + 5 ) = 375

2y² + 5y + 10y + 25 - 375 = 0

2y² + 15y - 350 = 0

By using

Roots of the quadratic equation formula,

⇒ y = -b ± √b²-4ac / 2a

⇒y = -15 ± √15²-4×2×-350 / 2×2

⇒y = -15 ± √3025 / 4

⇒y = -15 ± 55 / 4

⇒y = +40/4

⇒y = 10

y = 10, y cannot be ( -ve )

Gírl age is 2y, So we know that y = 10

= 2y

= 2 × 10

= 20 years

•°• Hence,

• Present Gírl age = 20 years
• Present of her sister's age ( y ) = 10 years