This answer is correct, so our calculation was correct.
Here is the option I prefer, however. Call out the problem backwards as an addition. This is probably
how you were taught to check subtractions in school. You add the answer to the number you subtracted
to get your original number as your check answer.
Adding the substitutes upwards, we get 6 + 8 = 14.
6 + 8 = 14
Adding the digits we get 1 + 4 = 5, so our calculation checks.
1 + 4 = 5
Our answer is correct.
I set it out like this:
Test yourself
Check these calculations for yourself to see if there are any mistakes. Cast out the nines to find any errors. If there is a mistake,
correct it and then check your answer.a) b) c) d)
They were all right except for b). Did you correct b) and then check your answer by casting the nines? The correct answer is 7,047.
This method will find most mistakes in addition and subtraction. Make it part of your calculations. It
only takes a moment and you will earn an enviable reputation for accuracy.
Note to parents and teachers
The difference is not so much with students’ brains but with the methods they use. Teach the strugglers the methods the high
achievers use and they can become high achievers too.