472 take away nine equals what?
How can we subtract nine in our heads quickly and efficiently? Well, the number nine is very close to 10. And subtracting 10 is very quick to do. What if we round nine to 10, subtract 10, and then adjust our answer? 472 take away 10 equals 462. But we’ve subtracted one more than we needed to. So we need to adjust our answer by adding one, which takes us to 463.
An even quicker way to find the same answer using the same method is not to visualise
a number line in our heads, but just to alter the digits. Look at how the numbers change. The tens digit decreases by one. Well, that’s the same as subtracting 10. And the ones digit increases by one. That’s the same as adjusting by adding one. And so subtracting 10 and then adding one is exactly the same as subtracting
nine. 472 take away nine equals 463.