[求助]prep2里面的数学~

1.A hiker walking at a constant rateof 4 miles per hour is passed by a cyclist traceling in the same direction along the same path at a constant rate of 20 miles per hour.The cyclist stops to wait for the hiker 5 minutes after passing her.while the hiker continues to walk at her constant rate.How many minutes must the cyclist wait until the hiker catches up?

答案：20

2.WheneverMarti has a restaurant bill with an amount between $10 and $99,he calculates the dollar amount of the tip as 2times the tens digit of the amount of his bill.If the amount of Martin’s most recent restaurant bill was between $10 and $99,was the tip calculated by Martin on this bill greater than 15 percent of the amount of the bill?（数据充分性）

（1）The amount of the bill was between $15 and $50

(2) The tip calculated by Martin was $8

答案B.

3.If@donates one of the tow arithmetic operations,addition or multiplication,and if K is an integer,what is the value of 3@K?（数据充分性）

(1)2@K=3

(2)1@0=K

答案：A

4.Is xy>0?(数据充分性)

(1)x-y>-2

(2)x-2y<-6

答案：C

Q1. distance= 20*(5/60)- 4*(5/60)miles

  speed =4 mile/hr

time=4/12 hr= 20min 很狡猾的一题哦。月亮走啊我也走的说。。。

Q2.so possible tips= 2,4,6,....18

for 1, it can be , for example, 2/15( <15%), or 4/20 (>15%), we can not tell

for 2, if we know the tip =8

the bill must be  40<x<50  all <15%, so we can tell and say, No ~~

Q3. for 1, 2+1=3 or 2x1.5=3, since integer, k must be 1, @ must be +, so it is fine

for 2,1+0=1, 1x0=0. two possible ， two possible @, so can not

Q4. for xy>0

x>0,y>0     or x<0,y<0

for 1, we cant  confirm

for 2, we also cant confirm

so we need to see if the inequalities can be solved. we try , and it does. so C

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