Answer: girls=20, sister=10
Step-by-step explanation:
Let x = the girl's sister's age (present)
Let 2x= the girl's age (present)
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According to the question
(x+5)(2x+5)=375
Expand parentheses by FOIL (First Outer Inner Last)
2x²+5x+10x+25=375
Combine like term (5x and 10x)
2x²+15x+25=375
Subtract 375 on both sides
2x²+15x+25-375=375-375
2x²+15x-350=0
Find the factors (cross factor)
(x-10)(x+17.5)=0
x=10 or x=-17.5 (rej) ⇔ the age can't be negative
the girl's age is 20, and her sister's age is 10.
