Math
posted by Mike .
Hi,I need to know how to do question like this without using a calculator. Can anyone help please.
Which of the following is closest to square root of 4000
A)40 B) 60 C) 200 D) 2000
I know the answer is B , but I did it on the calculator. Can someone show me how to get the answer by not using calculator.... Thanks a lot

Multiply the first digit by itself and add the appropriate zeros
40 * 40 = 1600 (4 * 4 + 00)
60 * 60 = 3600
200 * 200 = 40,000
2,000 * 2,000 = 4,000,000