求解4道MATH 题,谢谢!

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.

                  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

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

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?

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。

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。

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