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Current time:0:00Total duration:3:39

Multiplying fractions word problem: muffins

CCSS.Math:

Video transcript

a recipe for banana oatman's calls for 3/4 of a cup of old-fashioned oats you are making one half of the recipe how much oats should you use so if the whole recipe requires 3/4 of a cup and you're making half of the recipe you want half of 3/4 right you want half of the number of old-fashioned oats as the whole recipe so you want one half you want one half of 3/4 one half of 3/4 so you just multiply 1/2 times 3/4 and this is equal to you multiply the numerators 1 times 3 is 3 2 times 4 is 8 and we're done you need 3/8 you need 3/8 of a cup of old of old-fashioned oats and let's visualize that a little bit just so it makes a little bit more sense let me draw what 3/4 looks like or essentially how much oats you would need in a normal situation or if you're doing the whole recipe so let me draw let me draw let's say this is represents a whole cup and if we put it into fourths so let me divide it a little bit better so if we put it into fourths you put it into fourths 3/4 3/4 would represent three of these so it would represent one two three it would represent that many oats now you want half of this right because you're going to make half of the recipe so we could just split this in half we could just split this in half let me do with this with a new color so this this you would normally use this orange amount of votes but we're going to do half the recipe so you'd want half as many oats so you'd want half as many oats so you would want this many oats this many oats now let's think about what that is relative to a whole cup well one way we can do it is to turn each of these 4 buckets or these 4 pieces or these 4 sections of a cup into 8 sections of a cup let's see what happens when we do that so we're essentially turning each each piece each fourth into 2 pieces so let's divide each of them into two so this is the first this is the first piece we're going to divide it into two right there so now it is two pieces and then this is the second piece right here we divide it into one piece and then two pieces this is the third piece so we divide it into one two pieces and this is the fourth piece or the fourth section we divide it into two sections now what is what is this what is this as a fraction of the whole well we have eight pieces now right one two three four five six seven eight because we turn each of the four we split them again to eight so we have eight as a denominator and we took half of the three fourths right remember three fourths was in orange let me make this very clear because this drawing can get confusing this was three fourths right there so that in that is three fourths this area this area in this purple color this area in this purple color is one-half of of the three fourths but let's think about it in terms of the eighths how many of these sections of eight is it well you have one section of eight here two section of eights there three sections of eight so it is three eighths so hopefully that makes some sense or gives you a more tangible feel for what it means when you take 1/2 of three fourths