GWD2-21 & GWD2-gmat11

[vincemeagei]

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The figure shown represents a board with 4 rows of pegs, and at the bottom of the board are 4 cells numbered 1 to 4. Whenever the ball shown passes through the opening between two adjacent pegs in the same row, it will hit the peg directly beneath the opening. The ball then has the probability 1/2 of passing through the opening immediately to the left of that peg and probability 1/2 of passing through the opening immediately to the right. What is the probability that when the ball passes through the first two pegs at the top it will end in Cell 2?

A. 1/16
B. 1/8
C. 1/4
D. 3/8
E. 1/2

We dont know how to do it ?

If xy 0, is x/y = 1?
(1) x2 = y2
(2) xy > 0

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.

your explaination was greatly appreciated.
vince & meagei

[vincemeagei]

can somebody help plz~

[QQcandy]

21.

for (1) X2=Y2...X. Y may possible be positive or nagative...so can't decide if X/Y equel 1

for (2) XY >0, X>0 and Y>0 or X<0 and Y <0, that is, X and Y 同號 but can't tell if X = Y, so it's not sufficient...

However, if we combine both (1) and (2), we can make sure whether X/Y = 1

Hope it's clear...

[u9069700]

我也有相同的疑問~不知可不可以解釋一下 gwd2-11
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• • • 四顆
• • • • 五顆
׀ ׀ ׀ ׀
1 2 3 4

The figure shown represents a board with 4 rows of pegs, and at the bottom of the board are 4 cells numbered 1 to 4. Whenever the ball shown passes through the opening between two adjacent pegs in the same row, it will hit the peg directly beneath the opening. The ball then has the probability 1/2 of passing through the opening immediately to the left of that peg and probability 1/2 of passing through the opening immediately to the right. What is the probability that when the ball passes through the first two pegs at the top it will end in Cell 2?

A. 1/16
B. 1/8
C. 1/4
D. 3/8
E. 1/2

答案是D.....該如何求出來呢
我本來是用1/2*1/2*1/2=1/8
因為想說每遇到一個球瓶舊有兩各選擇:往右或往左，每各方向都是1/2的機會..不知道降有哪裡算錯了呢~感謝回覆喔!!!

[u9069700]

重新poㄧ次較詳細的圖喔~~降大家看的比較清楚....

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知道的朋友幫幫忙告訴我杯~~~感激

[u9069700]

ㄟ圖又歪掉了
怎麼降?

[u9069700]

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再發一次

[homaru]

http://www.formosamba.com/phpBB3/viewtopic.php?t=960
這一題問的跟以上連結的第17題一樣
cell1 and cell4機率一樣,都是(1/2)^3=1/8
cell2 and cell 3機率一樣,都是[1-2*(1/8)]/2=3/8

[ted186]

關於21.
2X=2Y,雖然XY可能為正或是為負,但應該是同時成立
也就是說當X為正,Y必為正---因此2X才會=2Y
我不懂A為什麼不行ㄟ

[vivid]

關於21.
2X=2Y,雖然XY可能為正或是為負,但應該是同時成立
也就是說當X為正,Y必為正---因此2X才會=2Y
我不懂A為什麼不行ㄟ

其實那是 X平方 跟 Y平方
不是2X 2Y

[micht]

21
If x is negative, is x < -3?
(1) x[sup]2[/sup] > 9
(2) x[sup]3 [/sup]< -9


這題答案是(A)阿 題目已經given X is negative

[Martina]

The figure shown represents a board with 4 rows of pegs, and at the bottom of the board are 4 cells numbered 1 to 4. Whenever the ball shown passes through the opening between two adjacent pegs in the same row, it will hit the peg directly beneath the opening. The ball then has the probability 1/2 of passing through the opening immediately to the left of that peg and probability 1/2 of passing through the opening immediately to the right. What is the probability that when the ball passes through the first two pegs at the top it will end in Cell 2?

A. 1/16
B. 1/8
C. 1/4
D. 3/8
E. 1/2

看了大家的討論 可是題目還是看不懂 可否解釋一下 ？？THANKS!!

[micht]

http://www.formosamba.com/phpBB3/viewtopic.php?t=960
這一題問的跟以上連結的第17題一樣
cell1 and cell4機率一樣,都是(1/2)^3=1/8
cell2 and cell 3機率一樣,都是[1-2*(1/8)]/2=3/8

夫子解釋的很清楚呀...

第一個凹 &第四個凹 掉進去的機率是一樣的
(1/2)[sup]3[/sup]*2=2/8(兩個凹的機率)
1-2/8=6/8
中間兩個凹平分6/8機率 (6/8)/2=3/8

Ans: D

[汪汪北鼻]

重新poㄧ次較詳細的圖喔~~降大家看的比較清楚....

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知道的朋友幫幫忙告訴我杯~~~感激

你的思考並沒錯，但想廣一點會有三條路徑直達Cell 2, illustrated as following
每一條都是1/2*1/2*1/2=1/8
Hence, 1/8*3=3/8

[pipson]

ㄟ.......
我想請問一下
為什麼球一定要從最上面兩個peg中間的洞丟下去啊
題目有這樣規定嗎??