请问类似这种问题是否有捷径.og 12

the product of all the prime numbers less than 20 is closest to which of the following powers of 10?

The answer is 10^7,

 OG : is 2x3x5x7x11x13x17x19=9699690...

any shortcut for the question ? Thanks

2x3x5x7x11x13x17x19

可以估算2*5=10

        3*7~20

         11~10

         13~10

         17~20

         19~20

估算后的数字相乘最接近 10^7  不过有时间的话，还是认真地算吧。。。