GWD 07-Q37

[jhchiou]

Q37: During a trip, Francine traveledx percent of the total distance at an average speed of 40 miles per hour and the rest of the distance at an average speed of 60 miles per hour. In term of x, what was Francine's average speed for the entire trip?

A. (180-x)/2
B. (x+60)/4
C. (300-x)/5
D. 600/(115-X)
E. 12,000/(X+200)

ans: E

想破頭還是解不出來, 救命啊!!!

[Jessy]

total distance=D
average speed=D/ {(DX/100)/40}+{D(1-X/100)/60}
=D/ {(DX/4000)+(100D-DX/6000)}
=12000/(X+200)

[Calvin]

entire trip average speed = entire distance / total time

assume: total distance = 1

total time = x%/40 + ( 1-x% )/60

then---> 1 / (x%/40 + (1-x%)/60) = 1/ ( 3X% + 2(1-x%))/120

= 120/ ( 2+x% ) = 120/ ( 2+x/100) = 120 / (( 200+X)/100)

then u got the answer

[jhchiou]

感激不盡!!!!
為什麼大家都這麼厲害......唉.....

[ktc]

total distance=D
average speed=D/ {(DX/100)/40}+{D(1-X/100)/60}
=D/ {(DX/4000)+(100D-DX/6000)}
=???

對不起，我不知道怎麼變成下面這個答案耶！
=12000/(X+200)

[/list]

[cheyen]

=D/ {(DX/4000)+(100D-DX/6000)}
=???

對不起，我不知道怎麼變成下面這個答案耶！
=12000/(X+200)

D/ {(DX/4000)+(100D-DX/6000)}

先處理DX/4000+100D-DX/60呀-->(2DX+4000)/24000
then
D/{(2DX+4000)/24000}
=12000/(X+200)
加油 別被計算打敗了 很不值得的

[ktc]

感謝你~~~耶！
有時就是要有人點一下才行！

[凱薩琳]

為什麼{D(1-X/100)/60} 會變成 (100D-DX/6000)

而不是D(1-X)/6000??

[Emilyh]

D/ {(DX/100)/40}+{D(1-X/100)/60}
=D/ {(DX/4000)+(100D-DX/6000)}
=12000/(X+200)

請問D(1-X/100)/60不是應該變成D-DX/6000，
為什麼會是100D-DX/6000?

[FrankChang]

為什麼{D(1-X/100)/60} 會變成 (100D-DX/6000)

而不是D(1-X)/6000??

應該是{D[1-(X/100)]/60}