Now we divide our answer, 390, by the second 6.
Six divides into 39 six times with 3 remainder (6 × 6 = 36). Write 6 below the 9 and carry the 3
remainder to make 30.
Six divides into 30 exactly 5 times, so the next digit of the answer is 5. Our answer is 65 with no
remainder.
I have written the problem the way I was taught.
If you prefer the other layout your calculation would look like this:What are some other factors we could use? To divide by 48, we could divide by 6, then by 8 (6 × 8 =
48).
To divide by 25 we would divide by 5 twice (5 × 5 = 25).
To divide by 24 we could divide by 4, then by 6 (4 × 6 = 24). Or we could divide by 3, then by 8, or
we could halve the number and then divide by 12.
A good general rule for dividing by factors is to divide by the smaller number first and then by the
larger number. The idea is that you will have a smaller number to divide when it is time to divide by the
larger number.
Dividing by numbers such as 14 and 16 should be easy to do mentally. It is easy to halve a number
before dividing by a factor. If you had to divide 368 by 16 mentally, you would say, ‘Half of 36 is 18,
half of 8 is 4.’ You have a subtotal of 184. It is easy to keep track of this as you divide by 8.
Eighteen divided by 8 is 2 with 2 remainder. The 2 carries to the final digit of the number, 4, giving
- Twenty-four divided by 8 is exactly 3. The answer is 23 with no remainder. This can be easily done
in your head.
If you had to divide 2,247 by 21, you would divide by 3 first, then by 7. By the time you divide by 7
you have a smaller number to work with.
2,247 ÷ 3 = 749
749 ÷ 7 = 107
It is easier to divide 749 by 7 than to divide 2,247 by 7.Division by numbers ending in 5
To divide by a two-digit number ending in 5, double both numbers and use factors. As long as you
double both numbers, the answer doesn’t change. Think of 4 divided by 2. The answer is 2. Now double
both numbers. It becomes 8 divided by 4. The answer remains the same. (This is why you can cancel
fractions without changing the answer.)
Let’s have a try: