求助:prep几道数学，非常感谢！！

南有樛木

有几道PREP里的数学，实在不会，请NN指教~~~

1) The rate of a certain Chemical reaction is directly proportional to 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 precent, which of the following is closest to the percent change in the concentration of Chemical  A required to keep the reaction rate unchanged?

答案：４０％ increase (不会，请帮我讲讲吧~）

2）If X and Y are integers greater than 1, is X a multiple o Y?

     i) 3y ^2 + 7y= x

     II) x^2 -x is a multiple of y

答案：A （不明白，请指教~）

3）Six machines , each working at the same constant rate, together can complete a certain job in 12 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 8 days?

答案：3 （还是不会~）

非常感谢各位NN~~

finebye

第一题是说这个Chemical reaction rate 的变化 同A成正比 同B成反比吧 B增加了100% A貌似也应该增加 我没算出来这个40% 不误导LZ了

第二题第一个条件给出了X的Y表达式 X/Y=3Y+7 正好证明X是Y的倍数啊 条件2有可能推出X-1是Y的倍数

第三题 设1=12*6*n 求出n后 代入 1=8*n*x 则x为9 增加3台

南有樛木

谢谢~~~ ^_^