Topic B: Division as an unknown factor problem
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- [Instructor] We are asked, which problem can we solve with 42 divided by seven? And they explain three different scenarios here. We need to pick one of them, so pause this video and have a go at it before we work through it together. All right, now let's work through this together. So let's see, choice A says, Steven packed 42 candy bars in his bag. He gave seven of them away to his friends. How many candy bars does Steven have left? Well, this isn't a situation of dividing. This is a situation where he starts with 42, and he takes seven of them away. So this would be the expression 42 minus seven, not the expression 42 divided by seven. Rule that one out. Julie has seven bags of jellybeans. There are 42 jellybeans in one bag. How many jellybeans does Julie have? Well, for each of those seven bags, she has 42 jellybeans. So this would be seven times 42, not 42 divided by seven. Rule that one out. Leslie ran for 42 minutes total in one week. If she ran the same number of minutes each day, how many minutes did Leslie run in one day? So she ran 42 minutes in total in the week, and she ran the same amount every day. There's seven days in a week. So if we wanna figure out how much did she run per day, you just divide the 42 minutes total divided by seven days in a week to figure out this would tell you right over here, how many minutes Leslie ran each day. And so that is the problem that we would solve with 42 divided by seven. Let's do another example. Here we are told Kaleb has 21 action figures. He puts three action figures in each box. What does the expression 21 divided by three represent? So pause this video again, and see if you can answer that. All right, so this is a situation where we're starting with 21, and we are dividing it into groups of three. So these are groups, groups of three. So this is going to tell us how many groups we need, if we're going to divide 21 into groups of three. So if I wrote 21 divided by three, and so this is groups of three, groups of three. This is going to be equal to something, and many of you might know what this is, but this is going to tell us how many groups, how many groups. And here a box represents a group. How many groups? So this is going to be the number of boxes. The number of action figures in each box, they already told us. There's three in each box, so that would be represented just by a three. The total number of action figures, that would be 21. The number of boxes is the total number divided by how many in each box. Let's do another one. Alex, Brian, and Marta split a box of 12 cookies evenly. Which expression helps us find out how many cookies each friend will receive? So pause this video again and see if you can tackle it. All right, so we're splitting 12 cookies. So we'll start with 12, and we need to divide it, and how many people are we dividing it between? Well we're dividing it between one, Alex, two, Brian, and three people, Marta. So we're going to divide it into three equal groups, and you might know what that is, but we don't even have to figure that out. We just have to say, hey, how many cookies does each of the three people receive? Well, it's going to be 12 divided by three cookies. So it is this choice right over here. Three divided by 12 doesn't make sense in this situation. You don't have three cookies, and you're not dividing it amongst 12 people, and C doesn't make sense. You're not just taking 12 cookies and dividing it between two people. You're dividing it between three people.