so if we do not know what 12 times 9 is then we can round 9 to 10 and get
12 times 10
most people can multiply by ten so this should be easy so
12 times 10=120
12 times 9=108
she was off by 12 so a 10% deviation error
another way to do it is you multiply 12 by 10 and get 10 12's
then you subtract 1 12 and get 9 12's