Four times 8 is 32, with −1 remainder, which we carry as −10, and we ignore the 9 for the moment.
We multiply 8 times + 1 to get + 8, which we add to the next digit, 9, to get 17, then we minus the 10
carried to get a remainder of 7.
With practice, this concept will become easy.Test yourself
Try these problems for yourself. Calculate to one decimal place.
a) 224 ÷ 29 =
b) 224 ÷ 41 =
Let’s calculate the answers together.We have divided both numbers by 10. Three divides into 22 seven times (3 × 7 = 21) with 1 remainder, which we carry to the next
digit, 4, to make 14. We multiply 7 × 1 = 7, and add to the 14 to get 21.
Now divide 21 by 3 to get 7, with no remainder to carry. Multiply the last digit of the answer, 7, by 1 to get 7, which we add to 0 for
our next working number. Seven divided by 3 is 2, with 1 remainder, which we carry to the next digit, 0, to get 10. We don’t need to
go any further because we only need an answer to one decimal place; 7.72 rounds off to 7.7. This is our answer.
Now for the second problem.We divide both numbers by 10. Four divides into 22 five times (5 × 4 = 20), with 2 remainder, which we carry to the next digit, 4, to
make 24. Now multiply 5 (the last digit of the answer) by −1 to get −5. Subtract the 5 from 24 to get 19.
We now divide 19 by 4 to get an answer of 4 with 3 remainder. The 3 carried gives us a working number of 30. Now multiply the
previous digit of the answer, 4, by −1 to get −4. Subtract 4 from 30 to get 26. Four divides six times into 26, and we can forget the
remainder. Our answer so far is 5.46. We can stop now because we only need one decimal place. Rounded off to one decimal place
we have 5.5 as our answer.
With practice, these calculations can easily be done in your head. Divide the last four digits of your
telephone number by different numbers in your head for practice. Try some other numbers as well. You
will find it is much easier than you imagine.