Have you ever wondered how much fish a seal can eat?
Jonah loves his job, especially because he gets to help feed the seals who live at the zoo. There are 25 female and 18 male seals for a total of 43 seals. One day, Ms. Guttierez, Jonah’s supervisor at the zoo, asked him to help her place the order for the week’s seafood. Jonah began to do some calculations. Each seal eats an average of 11 lbs. of seafood each day. The seafood comes in 25 lb. buckets. Jonah is puzzled. He doesn’t know how much food to order for one week. He doesn’t know how many buckets will be delivered. Jonah needs help.
In this Concept, you will learn how to help Jonah figure out his fish problem. How many pounds of seafood will they need to feed all of the seals for one week?
Now that we have learned about addition and subtraction, it is time for multiplying whole numbers.
Addition and multiplication are related. Hmmm... What does that mean exactly?
You can use your times tables to complete this problem using mental math, but let’s look at what we MEAN when we multiply 5 by 6. means that we are going to need five groups of six.
We could think of this another way too. We could add 5 six times.
Wow, that is a lot of work. It is easier to use our times tables.
When multiplying larger numbers, it will help you to think of multiplication as just a short cut for addition.
What about vocabulary for multiplication?
5 and 6 are factors in this problem.
What is a factor?
A factor is the name of each of the two values being multiplied.
30 is the product of the factors 5 and 6.
What does the word product mean?
The product is the answer to a multiplication problem.
Now let’s take what we have learned and look at how to apply it to a few more challenging problems.
If you think about this like addition, we have 567 added three times. That is a lot of work, so let’s use our multiplication short cut.
First, let’s line up our numbers according to place value.
To complete this problem, we take the digit 3 and multiply it by each digit of the top number. The three is called the multiplier in this problem because it is the number being multiplied. Since 7 is the first number in the upper row, we start by multiplying it by our multiplier, 3:
We can put the 1 in the ones place and carry the 2 (which is really two tens) to the next column over, where it can be added to the other tens after the next multiplication step.
Next, we multiply the 3 by 6 and add the two we carried. Leave the 0 in the tens place and carry the two.
Next, we multiply the 3 by 5 and add the two we carried.
Our product is 1,701.
Now let's look at one with more digits.
First, we need to line up the digits according to place value.
Our multiplier here is 12.
12 has two digits. We need to multiply each digit of the top number by each digit of the number 12. We can start with the 2 of the multiplier.
Next, we multiply the 1, which is in the tens place, by each digit. Because we are multiplying by a number in the "tens" place, we start the second row of numbers with a zero so that the answer to the multiplication is kept in the correct place value for the addition we will do next. Here is what this looks like.
Our product is 2,808.
You could multiply even more digits by more digits.
You just need to remember two things.
- Multiply each digit of the multiplier one at a time.
- Add in a zero for each digit that you have already multiplied.
Now let's practice. Multiply the following whole numbers.
Now back to Jonah and the seafood order.
We know from the problem that each seal eats an average of 11 lbs of seafood per day. We could do repeated addition here, add 11 forty-three times once for each seal. Boy that is a lot of work. When we have a repeated addition problem, our short cut is to multiply.
Jonah needs 473 pounds of seafood to feed all of the seals for one day.
That's great, but we need to feed all the seals for ONE WEEK! Once again, we could use repeated addition, but multiplication is so much quicker. There are 7 days in one week, so we can multiply 7 by the total pounds of seafood for one day.
Okay, we have helped Jonah with half of his problem. Now we know how much seafood he needs for one week.
Here are the vocabulary words used for this Concept.
the numbers being multiplied in a multiplication problem
the answer to a multiplication problem
the number you multiply with
Multiply the following values.
What about when we multiply three digits by three digits? First, you will multiply the first digit of the multiplier by each of the three digits of the top number. Second, you will multiply the second digit of the multiplier by all three digits of the top number. Don’t forget that placeholder zero! Third, you will multiply the third digit of the multiplier by all three digits of the top number. Use two zeros since you are now multiplying by a number in the "hundreds" place.
Our product is 77,468.
These videos will help you with multiplying whole numbers.
Khan Academy Basic Multiplication
James Sousa Example of Multiplying Whole Numbers
Directions: Use what you have learned to solve each problem.