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國二數學5題 - 10點

Jan 23rd 2014, 11:18

(1) 有兩列車(x,y)，一長92公尺，一長84公尺，相向而行，需時2秒，如一車追它車，自追及到超過需10秒，則分別求出這二列車的秒速？

Ans:

92+84=176=2*(x+y) => x+y=88

176=10(x-y) => x-y=17.6

Add: 2x=105.6 => x=52.8(m/s).....ans

y=52.8-17.6=35.2(m/s).....ans

(2) 小華的爸爸說：「我的年齡是二位數，將這二位數的個位數字與十位數字對調後，用3去除，再加上34，就等於我的年齡了」，那麼小華的爸爸是多少歲

Ans:

10x+y=(10y+x)/3+34 => 30x+3y=10y+x+102

29x=7y+102 => y(x)=(29x-102)/7

y(4)=2.....ans=42歲

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