GMATprep上的数学一道求教

uspresident

1 if n is a multiple of 5 and n= p²q, where p and q are prim numbers, which of the following must be a multiple of 25?

p²; q² ; pq; p²q²; p³q

the answer is p²q^2,

why?

2 When a certain tree was first planted, it was 4 feet tall, and the height of the tree increased by a constant amount each year for the next 6 years. At the end of the 6th year, the tree was 1/5 taller than it was at the end of 4th year. By how many feet did the height of the tree increase each year?

3/10

2/5

1/2

2/3

6/5

难道不应该用a1+(n-1)d这个公式算么？怎么算不出答案呢？　

我算法是４＋５d=6/5(4+3d) d=4/7

applebees

1.因为 n 是5的倍数，n= p²q, p和q 是质数

所以 P或q是5,

如果p是5,那么p^2等于25, p^2q^2 是25的倍数.

如果q是5,那么q^2 等于25,p^2q^2 是25的倍数