Eliminate Possibilities

Question

 

The square root of 7921 is a whole number. show using the technique of eliminating possibilities how you can determine this square root without a calculator?

Sample Questions for Final Exam: Comparing with others, Thanks

 

 

 

Answer 1

The tens digit must be 8 because the square is bigger than 6400 and less than 8100.

The ones digit is either 1 or 9 because the squares of 1 and 9 both end in 1. So we have 81 or 89 as the square root. Since 81 is only a little more than 80 and 7921 is close to 8100, 89 is likely to be the integer square root. In fact, 89²=7921.