求解4道MATH 题,谢谢!

cpcjustin

Q13:

Is the number of seconds required to travel d₁ feet at r₁ feet per second greater than the number of seconds required to travel d₂ feet at r₂ feet per second?

(1)     d₁ is 30 greater than d₂.

(2)     r₁ is 30 greater than r₂.

Q14:

Six cards numbered from 1 to 6 are placed in an empty bowl.  First one card is drawn and then put back into the bowl; then a second card is drawn.  If the cards are drawn at random and if the sum of the numbers on the cards is 8, what is the probability that one of the two cards drawn is numbered 5 ?

 A.1/6;   B.1/5;   C.1/3;   D. 2/5;  E.2/3

Q24:

                            y

 

                  S                            T

 

                                            U

                                                   x

                        O

 

 

In the figure shown, line segments ST and TU are parallel to the x-axis and the y-axis, respectively.  What is the sum of the coordinates of point T ?

(1)     The y-coordinate of point U is 1.

(2)     The x-coordinate of point S is –5.

Q36:

If a and b are positive integers such that a – b and  are both even integers, which of the following must be an odd integer?

 

A.a/2;  B. b/2;  C. (a+b)/2;  D.(a+2)/2 ; E. (b+2)/2

answers: EDED

soniashi

第24题画图可解得 E （根据具条件画图）

36题 好像是少条件的。

14题，2/6，6/2，3/5，5/3，4/4； 所以是40%的可能性。

13题是不太明白

cpcjustin

sorry,when i copied the problem,the fraction was lost.

Q36:

If a and b are positive integers such that a – b and  a/b are both even integers, which of the following must be an odd integer?

soniashi

odd+odd=even

odd+even=odd

odd*odd=odd

odd*even=even

even*even=even

a-b, even, so, a,b both even or odd

a/b, even, so, a,b both even,

到这里就可以举特例，a=2,b=2; 选项 ABCE都不成立了。而因为a/b, even,则a不能是2，最小是4，所以D。

soniashi

仅有2能对此题造成特例，所以仅考虑2 的影响因素就好了。

cpcjustin

Q36:

If a and b are positive integers such that a – b and  a/b are both even integers, which of the following must be an odd integer?

A.a/2;  B. b/2;  C. (a+b)/2;  D.(a+2)/2 ; E. (b+2)/2

odd+odd=even

odd+even=odd

odd*odd=odd

odd*even=even

even*even=even

a-b, even, so, a,b both even or odd

a/b, even, so, a,b both even,

到这里就可以举特例，a=2,b=2; 选项 ABCE都不成立了。而因为a/b, even,则a不能是2，最小是4，所以D。

不理解!a/b, even, so, a,b both even.b can be odd, for example:a=6,b=3,a/b=2;a=12,b=3,a/b=4