请教两题如何求解？

invisiblewys

1.Running at their respective constant rates, machine X takes 2 days longer to produce w widgets than machine Y.  At these rates, if the two machines together produce 5/4 w widgets in 3 days, how many days would it take machine X alone to produce 2w widgets?

 

A.      4

B.      6

C.      8

D.     10

E.      12

Answer:

2.For a nonnegative integer n, if the remainder is 1 when 2ⁿ is divided by 3, then which of the following must be true?

 

 

I.                    n is greater than zero.

II.                 3ⁿ = (-3)ⁿ

III.               √2ⁿ  is an integer.

 

 

A.   I only

B.    II only

C.   I and II

D.   I and III

E.    II and III

 

 

I.                    n is greater than zero.

II.                 3ⁿ = (-3)ⁿ

III.               √2ⁿ  is an integer.

 

 

A.   I only

B.    II only

C.   I and II

D.   I and III

E.    II and III

 

 

happypigfy

2.For a nonnegative integer n, if the remainder is 1 when 2ⁿ is divided by 3, then which of the following must be true?

 

 

I.                    n is greater than zero.

II.                 3ⁿ = (-3)ⁿ

III.               √2ⁿ  is an integer.

这个题 还是带数好了 对于这种必然有结果的题 带数是最方面的

发现 提干成立的时候 n为偶数  所以答案选2和3正确 选e

 

 

I.                    n is greater than zero.

II.                 3ⁿ = (-3)ⁿ

III.               √2ⁿ  is an integer.

这个题 还是带数好了 对于这种必然有结果的题 带数是最方面的

发现 提干成立的时候 n为偶数  所以答案选2和3正确 选e

happypigfy

1.Running at their respective constant rates, machine X takes 2 days longer to produce w widgets than machine Y.  At these rates, if the two machines together produce 5/4 w widgets in 3 days, how many days would it take machine X alone to produce 2w widgets?

 

A.      4

B.      6

C.      8

D.     10

E.      12

Answer:

这个题可以列方程式 两个 然后解联立方程 设x每天生产xw产品 y每天生产yw产品

1-----w/xw-w/yw=2

2-----（5w/4）/(wx+wy)=3 但是我觉得简便方法就是往里面带数 答案e说 是12天 那么 x的生产效率是 每天w/6 产品 y是w/4 你会发现带进去刚刚好 考试的时候 往里面带数好了