GMAT Math

Please help with these 9 math questions! I know this will probably be very easy for you guys, but I'm stuck.

Please provide explanations as to why they are the correct answers...thanks!

Questions 4-6

questions 7 - 9

Someone please help! I'm taking my GMAT in two days!!

1. avg speed = total dist / total time;
2. put a and b in function and add them. then put (a+b) in function and see if sum matches.
3. no idea
4. 4c2 * 3c2
5. 24 = (2/3) * pi*D where D is diameter
6. no idea
7. 1/10 ..couldnt get any other solution.
8. no idea.
9. same as 1.

hope these tips help you.

nishuonly wrote: 2. put a and b in function and add them. then put (a+b) in function and see if
hope these tips help you.

I don't get it. Care to elaborate?

Thanks!

Edit: I can't seem to understand some of your answers. Can someone else help me?

I'm Chinese, so I don't know if I can explain it clearly.
2. ∵f(a)=2/a, f(b)=2/b,
∴f(a)+f(b)=2/a+2/b=2(a+b)/ab;
but f(a+b)=2/(a+b);
if a=2,b=4, then 2(a+b)/ab=3/2; 2/(a+b)=1/3; so D is wrong.
3. If we know both of them, then ∠RQS=∠RSQ, ∠TSU=∠TUS.
∵∠P=90 ∴ ∠R+∠T=90
and∵∠R=180-2∠RSQ ∠T=180-2∠TSU.
∴∠R+∠T=(180-2∠RSQ)+(180-2∠TSU)=90
∴ ∠RSQ+∠TSU=135, so ∠X=180-135=45.
Hope u can understand these~~

@lauyeung .. the reason you are not getting enough responses is because you have posted 9 questions on a single thread. Open separate threads for each of them and believe me you will get an excellent response. You are also breaking board rules by posting more than one question on a thread. Please do post these questions in separate threads in the appropriate section i.e. Problem Solving and Data Sufficiency. I am locking this thread.

Regards

PS:- Welcome to Beat the GMAT