Here is a trick for mental arithmetic when one of the numbers is close to a multiple of 10 or 100. Figure out how far you are from that "nice" number and move that many steps first. Then the remaining movement is much easier to do. Here’s a visualization of \(97 + 58\text{:}\)
Draw a number line diagram using the technique above to calculate \(98 + 77\text{.}\)
2.
Draw a number line diagram using the technique above to calculate \(49 + 36\text{.}\)
3.
Practice your mental arithmetic by performing the following calculations.
Which of the calculations did you find to be easier with this technique? Which were harder? What are the key differences that make one easier than the other?
