GMAT Quantitative Sample QuestionThe product of all the prime numbers less than 20 is closest to the following powers of 10?(A) 10^9 (B) 10^8 (C) 10^7 (D) 10^6 (E) 10^5请提供解题思路.比20小的质数有哪些我也知道。我想这道题如果用计算器来计算，结果就没什么意义了。如果是在纸上吭呲吭呲算出乘积来的，这方法未免太笨太费时了。有没有一个巧妙的方法
2019-04-02
GMAT Quantitative Sample Question
The product of all the prime numbers less than 20 is closest to the following powers of 10?
(A) 10^9 (B) 10^8 (C) 10^7 (D) 10^6 (E) 10^5
请提供解题思路.
比20小的质数有哪些我也知道。我想这道题如果用计算器来计算，结果就没什么意义了。如果是在纸上吭呲吭呲算出乘积来的，这方法未免太笨太费时了。有没有一个巧妙的方法可以得出正确答案来呢？
用对数可以解此题吗?
优质解答
2*3*5*7*11*13*17*19= 9699690
9699690 = 9.70 x 10^6 is about 10 x 10^6 = 10^7
the answer is C)
先把 2 3 5 7这四个10以哪的数字相乘,答案210,可以心算出来.
然后看11 13 17 19,用11*19,13*17,因为17,19接近20,大致能估算出乘积都是200左右的数字,210*200*200,不用具体算出来.看后面一共6个0,大致估计10^7是最接近的.
There is one thing you might want to know.Come on,I mean,that's just one simple question from GMAT.It was designed to test your ability academically in graduate business studies,not some sort of math contest.
2*3*5*7*11*13*17*19= 9699690
9699690 = 9.70 x 10^6 is about 10 x 10^6 = 10^7
the answer is C)
先把 2 3 5 7这四个10以哪的数字相乘,答案210,可以心算出来.
然后看11 13 17 19,用11*19,13*17,因为17,19接近20,大致能估算出乘积都是200左右的数字,210*200*200,不用具体算出来.看后面一共6个0,大致估计10^7是最接近的.
There is one thing you might want to know.Come on,I mean,that's just one simple question from GMAT.It was designed to test your ability academically in graduate business studies,not some sort of math contest.