Solving multi-step problems (multiplication): camping items
About this video
Twelve friends each pack 10 snacks and 3 water bottles. The video adds first to find 13 items per person, then multiplies 13 x 12 using the standard method to get 156 items in total. It also points out that the order of numbers in a word problem is not always the order you do the operations.
You'll be able to
- decide which operation to do first in a multi-step word problem.
- write an expression with parentheses, like 12 x (10 + 3).
- multiply a two-digit number by a two-digit number, like 13 x 12.
Key words
- parentheses
- Brackets ( ) that show which part of a calculation to do first.
- per person
- For each one person.
- ones place / tens place
- The positions of digits that show how many ones and how many tens a number has.
Transcript
- [Instructor] We're told a group of 12 friends pack supplies for a camping trip. Each person packs 10 snacks and three water bottles in their backpack. How many total items do they pack? So pause this video, have a go at this before we do this together. All right. Now let's do this together.
So there's a few ways I could approach it. We could say, "All right. I have 12 friends." And then, "How many items do each of those friends have?" And so however many items each of them have, I can multiply it by 12, and then I'll have the total number of items.
Well, it looks like each of them, they have two types of items. They have snacks and water bottles. So each of them packs 10 snacks and they also pack 3 water bottles. So what we'd want to do is first add the number of snacks to water bottles per person, per friend, and then multiply by 12.
I could write it in another order. The important thing is to realize that the order that is showing up in the word problem here, or in the description isn't necessarily the order that you do the operations in. So for example, I could add the 10 plus 3 first to figure out how many items does each person carry.
And then I would multiply that times the number of people. These two things are equivalent because of these parentheses. I'm adding the 10 plus 3 first in either case. So let's do that 10 plus 3. We can do that in our heads. This is going to be 13. And then we need to multiply 13 times 12.
And some of you might know what 12 times 12 is, and we just have to add one more 12 to that. But I'm just going to write it out to do it properly. So we want to multiply 13 times 12, so we can start in the ones place, at least on the the 12. So 2 times 3 is 6.
And then 2 times 1 is 2. Another way to think about it, 2 times 13 is 26. Now I'm going to go to the 10s place, at least on the 12 here. And so I'm gonna put a 0 here. So 1 times 3 is 3. 1 times 1 is 1. And another way to think about it, I just multiplied 10 times 13, which is indeed 130.
And now I can just add things. Six ones plus zero ones is six ones. Two tens plus three tens is five tens. And then I have that 100 there. So I get 156 is the total items that they pack. So this is equal to 156 and we're done.
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