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Current time:0:00Total duration:3:19

Subtracting fractions word problem: tomatoes

CCSS.Math:

Video transcript

Silvia's growing tomato plants and studying their heights here is her data so the beefsteak tomato type had a height of 3 3 and 1/4 feet roma 2 and 7/8 feet cherry 3 and 1/2 feet and they asked us what is the difference between the heights of the beefsteak between the heights of the beefsteak so that's that one right over there and the Roma and the Roma tomato plants so they want us to find the distance between these two heights so this cherry tomato height this was really unnecessary for the sake of this problem so we want to find the difference in this these two heights so we want to subtract the smaller of these from the larger of these so we're really trying to evaluate what 3 and 1/4 minus 2 and 7/8 is minus 2 and 7/8 now the first thing that I like to do is convert both of these into mixed numbers so let's store it sorry they're already mixed numbers to convert both of these into improper fractions so 3 and 1/4 is the same thing as 3 plus 1/4 which is the same thing as 12 forts 12 forts plus 1/4 that's the same thing as 3 and 1/4 and from that we're going to subtract 2 and 7/8 2 and 7/8 is the same thing as 2 plus 7/8 2 is the same thing as 16 over 8 plus 7 over 8 so this is essentially what we are trying to figure out now what is 12 fourths plus 1/4 it's thirteen fourths 13 over 4 and then what's 16 8 plus 7 8 well that's 23 over 8 so this is going to be minus 23 over 8 now we're subtracting to or subtracting one fraction from another but we have different denominators so we can't make sense of this until we have the same denominator and so what is the least common multiple of these two denominators of both 4 and 8 what is the smallest number that is divisible by both 4 & 8 well 8 is divisible by 8 and 8 is also divisible by 4 or so if we can rewrite 13 over 4 as having 8 as a denominator then we are all set so let's try to do that so we're going to write both of these as 8 with 8 as a denominator this one already has it so 13 over 4 I'm going to have it with 8 as a denominator so if we multiplied the denominator to get from 4 to 8 we have to multiply the denominator by 2 so in order to not change the value of the fraction we have to multiply the numerator by the exact same value we got to multiply it by 2 so this becomes 26 over 8 and from 26 over 8 we're going to subtract 23 over 8 and so this is going to be over 8 26 26 - 23 - 23 which is equal in too and we deserve our drumroll now 26 minus 23 is 3 so it's 3/8 so the difference between the heights of the beefsteak and and Roma tomato plants 3/8 and everything we've been doing in so far has been in feet so 3/8 of a foot