Help!--prep practice 1 maths

ilovemaple2

Can anyone help with the following prep questions? thanks a million~

1.The rate of a certain chemical reaction is directly proportional to the square of the concentration of chemical A present and inversely proportional to the concentration of chemical B present.If the concentration of chemical B is increased by 100%, which of the following is closest to the percent change in the concentration of chemical A required to keep the reaction rate unchanged?

the answer is 40% increase.

2.If the integers a and n are greater than 1 and the product of the first 8 positive integers is a multiple of a^n, what is teh value of a ?

(1)a^n=64   (2)n=6

The answer is B.

搞不懂怎么做，请教各位啦~

3.For all positive integers m, (m)=3m when m is odd, (m) is 0.5m when m is even, which of the following is equivalent to (9)*(6)? 我觉得是81啊，答案是27。还是Gmac的官方模考的题，难道答案错啦？