Question

Explain how using basic facts can help you find 10x20x30x40 mentally.

Answer 1

To multiply

10×20×30×40

As we can see that each number has a zero at end.

So we can count the total number of zeros , as here we count there are 4 zeros.

Now we multiply the numbers other than zeros of the number.

So

1×2×3×4

1 times 2 is 2

2 times 3 is 6

And

6 times 4 is 24

Now behind this result we put the number of zeros we counted.

4 zeros

Hence we get

240000 as final result.

So final answer is 240000, this is how we do it mentally.

Answer 2

As each number has a four zero at end.

Now we multiply the numbers other than zeros of the number.

Hence 1 × 2 × 3 × 4 = 24

Now,  we have to put the number of zeros we counted.

That is 4 zeros should be placed.

Hence, we will get 240000 as final answer.