PREP 里几道数学， 各位帮帮忙 好吗？

sydneyang

Sorry to ask so many at a time. Really hope someone could help, as I tried and couldn't

figure out WHY!!!  Thanks in advance.

1）  In the xy-plane, does the line with equation y=3x+2 contain the point (r,s) ?

a)       (3r+2-s)(4r+9-s)=0

b)       (4r+6-s)(3r+2-s)=0

Key:C

       I thought D

 

2)  A constuction company was paid a total of 500,000 for a job. The only costs are labor and materials. Was the company's profit greater than 150,000?

         a)  Company's total cost was 3 times it's cost for materials.

         b)  The company profit was greater than its cost labor.

                   Key:C

        I thought E

 

3)  If Bob produces 36 or fewer items in a week, he is paid X dollars per item. If Bob produces more than 36 items in a week, he is paid X dollars per item for the first 36 items and 3/2 times that amount for each additional item. How many items did Bob produce last week?

         a)  Last week, Bob was paid a total of $480.

         b)  This week Bob produced 2 items more than last week and was paid a total of $510.

              Key: E

              I thought C

 

4)  If n and t are positive integers, what is the greatest prime factor of the product nt ?

         a)  The greatest common factor of n and t is 5.

         b)  The least common factor of n and t is 105.

             Key: B

             I thought D

sydneyang

Thanks for your help. But I still don't get it. I am math dummie.

Could you further explain why "4r+9-s=0产生的(r,s)不满足y=3x＋2".

I guess i don't see the relationship of the statements given to the problem itself.

Many thanks...if you could explain...

sydneyang

Hee....Sorry.

It should read: "The least common multiple of n and t is 105.

Btw, i got the other problems, thank YOU.

sydneyang

nn,

FINALLY, I GOT THEM ALL! YEAH...

THANK YOU, THANK YOU, and Thank You.