How would you use this method to solve 34 × 76?
One method would be to use 30 as a reference number and use factors of 2 × 38 to replace 76. You
could also solve it directly using direct multiplication. Here is how we do it:
We will multiply from right to left (as is most common), and then try it again from left to right.
Firstly, we begin with the units digits:
6 × 4 = 24
We write the 4 and carry the 2. Then we multiply crossways and add the answer.
7 × 4 = 28
3 × 6 = 18
28 + 18 = 46
(To add 18 you could add 20 and subtract 2.)
Add the carried 2 to get 48. Write 8 and carry 4.
Now multiply the tens digits:
3 × 7 = 21
Add the 4 carried to get 25. Now we write 25 to finish the answer. The calculation was really done
using traditional methods but written in one line. The finished calculation looks like this:
Here are the steps for this problem:
6 × 4 = 247 × 4 = 28
3 × 6 = 18
28 + 18 + 2 carried = 487 × 3 = 21 + 4 carried = 25Each digit is multiplied by every other digit. The full working looks like this:Solving from right to left is probably easiest if you are using pen and paper. If you want to solve the
problem mentally then you can go from left to right. Let’s try it.
Thirty times 70 is 3 × 7 × 100. The 100 represents the two zeros from 30 and 70.
3 × 7 = 21
21 × 100 = 2,100
I would say to myself, twenty-one hundred.