Multiplication Trivia!

multiplication-trivia

Sometimes, trivial questions lead to in-depth understanding of the subject.
A few days back, one of my Primary 4 students asked a Multiplication Trivia.

33
× 22
=======
66
660 ⬅
========

Why do we put a zero in the second row of multiplication ?

I was very happy with the fact that my students are getting inquisitive.

We sat down together to understand the logic behind this zero and it took him hardly 5 mins to get the answer.

When we multiply 33 by 2 (units place), the answer is 66. But when we multiply 33 by the other 2 (tens place) we are actually multiplying it by 20. ( look at the place value of this 2)
Hence, we need a 0 in the second row. (see arrow)

Similarly, we will need 2 zeros in the third row if there are 3 digits, and so on. Simple, right?

It is very important for us to motivate our children for asking questions.

No question is too simple.

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