Today's Maths Investigation

Some Number Magic?

This is a great way to practice addition and subtraction of two digit numbers.  I have found students will stick at a task like this for longer than doing a page of exercises from a Math(s) Book

•Choose any number between 50 and 99

                                                                  

•Add 62 to this number

                                                                  

•Cross off the left hand digit (hundreds digit) of the result and add it to the units digit.

                                                                    

•Subtract the result from your original number

                                                                     

•Try it again with a different starting number

•What do you notice?

•Can you think why this always happen?

•Now work out how you can choose a number

(between 50 and 99) and add a special number, so

that when you cross off the left hand digit (hundreds

digit) of the result and add it to the units digit and then

subtract the result  from your original number you will arrive at 45.

I think my students enjoyed this investigation. They've had to add and subtract, and we've had opportunities to discuss the language of Mathematics, Place Value, and much more.

Nobody could explain why it works, or how to arrive at 45... apart from one parent. Well done, Kerry.

Kerry used a strategy called "Trail and error". She tried several ideas and... did not give up. Something all mathematicians have in common.