One of the common problem in doing mental multiplication is many students forget that multiplying larger numbers quickly requires breaking those larger numbers into more practical pieces. For example, if we see
17 x 6
you might think that 17 is a huge number and difficult to multiply.
To simplify the problem, you can break 17 into two manageable numbers that you can both multiply times 6. To get the right answer, add the result of two numbers. You might take 9 and 8, (9×6)+(9×8). But there is an easier way i.e. to choose a number which ends in a zero as these numbers are easiest to multiply.
Let’s take the example of 17. It can be broken into
7 + 10= 17
Now multiplying the 6 by 10 is quite instantaneous.
10 x 6= 60
That leaves the 7 thus giving us
7 x 6 = 42
Now add both values
42 + 60 = 102
An important point to consider is that not to think of this as a writing exercise. Simply make these equations in your mind and breaking these numbers in this way will make things quite easier for you. While doing this, you multiply 10×6 and then keep 60 on hold, then you multiply 6×7 and finally add both 60 and 42.
Let’s solve another equation with slightly larger number
Suppose we have
32 x 8
One way you can follow is to multiply 10×8 three times. But a faster way is to multiply
30 x 8
We have selected 30 as it ends in zero and closest to 32. This gives us 30×8 which is same as 3×8 with a zero at the end.
3 x 8= 24
Now add zero and it will give
Now we will put this number on hold and multiply the 2 left over as our original number was 32 time the 8. So,
2 x 8=16
The final step is to add this number to the on-hold number i.e. 240
Have a great test day with making the complex multiplications way too simpler for you.