GMAT数学(博智教材)第62页:If X is equal to the sum of the even integers from 40 to 60, inclusive, and y is the number of even integers from 40 to 60, inclusive, what is the value of x+y?
X=40+42+44......60=550
Y=(60-40)/2+1=11, 答案应该是561,为什么书后面的答案显示是560?
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题目:A Printer numbered consecutively the pages of a book, beginning with 1 on the first page. In numbering the pages, he printed a total of 189 digits. How many pages are there in the book?
问题:看了中文翻译并听了管老师的讲解,我都没弄明白这个题目的解题思路。的别是对“a total of 189 digits”的处理。
题目:If n is a prime number greater than 3, what is the remainder when n的平方is divided by 12?
问题:当管老师解题时,他出了3个方程式,分别是:
1) n=3A+1, n的平方=9A(square)+6A+1
2) n=3A+2, n的平方=9A(square)+12A+4
3) n=2A+1, n的平方=4A(square)+4A+1
我不明白的点是:这3个方程式是怎么推到或者是一看到题目就这么设出来的?