PREP2 两道DS求助

阳光桂公主

If 500 is the multiple of 100 that is closest to x and 400 is the multiple of 100 that is closest to y, which multiple of 100 is
closest to x + y ?
(1) x < 500
(2) y < 400
答案是E

A store purchased 20 coats that each cost an equal amount and then sold each of the 20 coats at an equal price. What was
the store's gross profit on the 20 coats?
(1) If the selling price per coat had been twice as much, the store's gross profit on the 20 coats would have been $2,400.
(2) If the selling price per coat had been $2 more, the store's gross profit on the 20 coats would have been $440.

答案是B

求解，求解，怎么也想不明白

sdcar2010

multiple of 100: 100, 200, 300, 400, 500, 600, . . .

Among the above candidates, 500 is the closest to x and 400 is the closest to y. Do you know which of the above numbers is closest to x+y?

Premise:  450<x<550 and 350<y<450

condition 1) 450<x<500, 800<x+y<950.  The multiple of 100 could be 800, 900,
condition 2) 350<y<400, 800<x+y<950.  The multiple of 100 could be 800, 900
conditions 1) and 2) 450<x<500, 350<y<400, 800<x+y<900. The multiple of 100 could be 800, 900.

sdcar2010

A store purchased 20 coats that each cost an equal amount and then sold each of the 20 coats at an equal price. What was
the store's gross profit on the 20 coats?
(1) If the selling price per coat had been twice as much, the store's gross profit on the 20 coats would have been $2,400.
(2) If the selling price per coat had been $2 more, the store's gross profit on the 20 coats would have been $440.

Coat was bought at price $x and sold at price $y. Ask for the profit = 20*(y-x)

1) 20*(2y-x) = 2400. Two unknowns, one equation, not sufficient to sove both x and y, and not sufficient enough to sove (x-y).
2) 20*(y+2-x) = 440. Two unknowns, one equation, not sufficient to solve both x and y, but sufficient enough to solve (x-y)

1) and 2) together: Two unknowns, two equations, sufficient.

CCCCCCCCCCCCCCCCc

BBBBBBBBBBBBBBBBBBBBBBBB

If the second condition changes to:

(2) If the selling price per coat had been $2 more, the store's gross profit on the 20 coats would have been increased by 10%.

The answer is B.

bbltxl

选B，题目求的就是y-x

A store purchased 20 coats that each cost an equal amount and then sold each of the 20 coats at an equal price. What was
the store's gross profit on the 20 coats?
(1) If the selling price per coat had been twice as much, the store's gross profit on the 20 coats would have been $2,400.
(2) If the selling price per coat had been $2 more, the store's gross profit on the 20 coats would have been $440.

Coat was bought at price $x and sold at price $y. Ask for the profit = 20*(y-x)

1) 20*(2y-x) = 2400. Two unknowns, one equation, not sufficient.
2) 20*(y+2-x) = 440. Two unknowns, one equation, not sufficient.

1) and 2) together: Two unknowns, two equations, sufficient.

CCCCCCCCCCCCCCCCc

If the second condition changes to:

(2) If the selling price per coat had been $2 more, the store's gross profit on the 20 coats would have been increased by 10%.

The answer is B.

-- by 会员 sdcar2010 (2011/4/3 19:24:29)

阳光桂公主

好难好难啊

阳光桂公主

第二道题选B

20(y+2-x)=440能求出20（y+x)=400

阳光桂公主

第一题还是不太明白啊。。为什么500 is close to x,       450<x<550呢？？