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作者: jilin1960 時間: 12-5-23 18:21 標題: 請教數學題

Jeff is on the middle step of a ladder .there are the same numbers of steps above and below him.Jeff goes down 2 steps ,up 5 steps ,then down 9 steps .He is now on the bottom step of the ladder .How many steps does the ladder have?

小兒的答案是12

the step Jeff is standing is A

A-2+5-9=0
A=6

2A=12

請問錯在哪裡﹖謝謝﹗

作者: cornelius 時間: 12-5-23 18:25

本帖最後由 cornelius 於 12-5-23 18:28 編輯

回復 jilin1960 的帖子

Should the answer be 13, since there are the same no. of steps above and below (that means the no. of the steps of the ladder would be an odd no.) ?
Let the step on which Jeff stood originally be the Ath step. Then,

A-2+5-9=1
A=7

So there are 6 steps below. Similarly there are 6 steps above the 7th step. Hence the no. of steps would be 6+1+6 = 13.

作者: marcuscyrus 時間: 12-5-23 18:25

本帖最後由 marcuscyrus 於 12-5-23 18:28 編輯

jilin1960 發表於 12-5-23 18:21
Jeff is on the middle step of a ladder .there are the same numbers of steps above and below him.Jeff ...

bottom step=step1 or step 0?
如=step 1, 他在step 7, 上下各有6，no of steps =13
如=step 0, 他在step 6, 上下各有5, no of steps=11?

作者: jilin1960 時間: 12-5-23 21:08

謝謝﹗明白了。

作者: LL222 時間: 12-5-30 19:20

一睇題便知一定係單數，雙數點企中間啊

作者: JustAParent 時間: 12-5-30 20:52 標題: 回覆：請教數學題

估計是小二、三的題目，要用代數嗎？站在梯中間，最後到了最低一級，即向上為「-」，向下為「+」，2-5+9=6 （小二教過加減交換次序的）向下有6級，向上也是6，6+6+1=13。

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