In yesterday's post we looked at prime and composite numbers and using the order of operations to simplify expressions. If you missed the live stream of the answers, you can watch that here. Today we move onto the largest and most important of the four reporting categories (sections) of the 5th grade math curriculum - computations and algebraic relationships.
Multiplying 3-digit by 2-digit Numbers
In 4th grade, students learned to multiply 2-digit numbers in a variety of ways, including arrays, area models, partial products, and the standard algorithm. In 5th grade, we forget all that fancy stuff and drill down to the standard algorithm, or what parents call, "How I learned to multiply!" The video below shows the standard algorithm on the left and partial products (using place value) on the right to explain why, in the standard algorithm, students always place a 0 in the ones place of the second row.
Without using a calculator, try this practice problem from a released STAAR test. Be careful - there's a trick!
Multiplying Decimals
Now that boring, whole number multiplication is out of the way, let's look at something new to 5th grade. Students will need to learn to multiply decimals. The multiplying part is easy but finding the correct place to put the decimal point in the product can be tricky. This first video shows, using area models, what actually happens when you multiply decimals.
With that information in mind, now you can move on to multiplying decimals without using area models.
Decimal multiplication is just like whole number multiplication except for placing the decimal point in the product. Now that you know how to do that, try these two problems from a released STAAR test.
Correct Answers
Tonight (3/25/20) at 8:00 pm (CDT), I'll live stream from my YouTube channel to go over the answers to these three practice problems. Make sure you've already worked them out ahead of time. I can answer questions you might have in the stream chat and I'll put the recording on my channel and in this post for anyone that couldn't watch it live. If you haven't done so already, you can subscribe to the channel to get notifications for live streams and new videos that I post.
Here's the live stream with the answers and explanations.