a girl is twice as old as her sister .five years hence the product of their ages in yrs will be 375 .find their present ages.
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ATQ, a girl is twice as old as her sister.
let her sister's age be x
therefore her age = 2x
5 years after, the product of their ages will be 375
➡ (5 + x)(5 + 2x) = 375
➡ 5(5 + 2x) + x(5 + 2x) = 375
➡ 25 + 10x + 5x + 2x² = 375
➡ 25 + 15x + 2x² = 375
➡ 2x² + 15x = 375 - 25
➡ 2x² + 15x = 350
➡ 2x² + 15x - 350 = 0
using splitting middle term method,
= 2x² + (35x - 20x) - 350
= 2x² + 35x - 20x - 350
= x(2x + 35) - 10(2x + 35)
= (2x + 35) (x - 10)
equating both factors by 0
2x + 35 = 0
➡ x = -35/2
x - 10 = 0
➡ x = 10
since age can't be negative.
hence, her sister's age is = x =10 years
and her age is = 2x = 2 × 10 = 20 years
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