The standard multiplication algorithm with a two-digit multiplier — aka two-digit multiplication and why we add a zero on the 2nd line

I explain how to multiply by a two-digit number (standard multiplication algorithm). This involves two separate multiplications and lastly adding their results. In the second multiplication, one has to add a zero in the ones place. This is because we're actually multiplying by a multiple of ten (such as 70 or 40). (I explain that more in this video.)

In this second part, we take a look at a word problem that gives info for the wages of two persons (Mathy my mascot and Abby) and asks who earns more in a week, and how much more. We need to use 2-digit multiplication to solve it.

See also

Use mental math (partial products) to multiply

Math Mammoth Grade 4 curriculum

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