How to estimate a difference?

Question

I have a doubt what is the estimated difference of $91-45$ so I started to think about two methods the first was I will first find the difference of $91-45$ that is 46 than I will just round off 46 nearest tens so I got 50 as my answer.my second method is first I would round off 91 nearest tens so I got 90 than I would round off 45 nearest tens so I got 50 than I would subtract 50 from 90 so I got 40.Which method is correct?

Answer 1

This depends on the definition provided. Both are correct but the most accepted one is the second one in most cases.

Remember it is just an estimate and it doesn't matter much but if you ask from an examination view. You can ask your instrucor. I follow the second method.