This activity helps us practice multiplying numbers in columns. You will need a stopwatch, paper, and a pencil. (Instead of a stopwatch, you can use an ordinary watch or clock with a second hand. Just be sure to keep careful track of the time!)
This activity allows you to note the time you spend when multiplying two-digit numbers by single-digit numbers.
You must remember that when multiplying two-digit numbers by single-digit numbers, we are actually solving two multiplication problems. We start with the ones place (ones column) first and solve the tens place (tens column) next. Then we add the answers for the ones and tens problems to get our answer.
But we also know that there is an easy way to work multiplication problems without doing the ones and tens problems separately. This time, our solution involves regrouping (carrying). The first digit of the product to the problem in the ones place is regrouped to the tens place like this:
Then we work the tens place. The answer we get is added to the tens we carried earlier. Finally we have our answer.
Now, here's what to do:
First, you will work the problem below by solving the ones and tens problems separately. Get your paper and pencil and start solving now. Don't forget to set that stopwatch!
How long did it take you to finish solving the problem?
Next, solve the same problem below by regrouping. Let's find out which way you finish the fastest. Don't forget to reset your stopwatch!
In which way are you faster at multiplying two-digit numbers?
Ready to move on to the next lesson?
Column Multiplication with Tens
