3-by-3 and 3-by-4 digit multiplication, plus word problems (5th grade math

I explain how to do a 3-by-3 digit multiplication problem (traditional algorithm), and why we put a zero at the end of the 2nd line, and two zeros at the end of the 3rd line. A grid paper can help with these types of problems!

I show a quick example of how to do a 3-by-4 digit multiplication problem. Again, we put a zero at the end of the 2nd line, and two zeros at the end of the 3rd line. A grid paper can help with these types of problems!

Next in this lesson, we review how to multiply numbers that end in lots of zeros, such as 50 × 3,000. We also practice this backwards: what times 40 makes 320,000?

Then it's time for a word problem: how many seconds are in a day? We start out by noting there are 60 seconds in a minute. This ends up being a multi-digit multiplication problem, but because of the zeros, it's not too complicated (actually just 2-digit by 2-digit multiplication).

The last example is a word problem that has to do with a money amount. Mr. Jefferson spends $2.50 on coffee every working day. How much does he spend on it in a year? He takes a 4-week vacation yearly. We need to use multiplication... and consider the working days in a week, and the number of weeks in a year.

See also

Long division with a two-digit divisor

Multiplying in Parts

Math Mammoth Grade 5 curriculum

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