MATHS!!!!!

👨🏻‍🏫 學術台數學

handsome

2008-12-29 6:22 pm

John is 2years older than his brother Tom,but 28 years younger than
his mother Jenny.Three years later,Jenny's age will be exactly the
product of her sons'.How old is Jenny now?

回答 (4)

用戶8785

2008-12-29 6:59 pm

✔ 最佳答案

Let Y be Jenny's age
Y + 3 = (Y - 28 + 3)(Y - 30 + 3)
Y + 3 = (Y - 25)(Y - 27)
Y + 3 = Y^2 - 52Y + 675
0 = Y^2 - 53 + 672
0 = (Y - 32)(Y -21)
Y = 32 or 21 (rejected, Jenny is 28 years older than John..)

Therefore, Jenny is 32 years old now.

參考: myself.. 勿抄!!

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Gladys

2009-01-02 6:43 pm

Let X be John's age.
After 3 years, (X+3)*(X-2+3)=X+28+3
X^2+4X+3=X+31
X^2+3X=28
X=4
So Jenny is 32 (4+28) now.

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