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Dividing whole numbers by decimals examples

CCSS.Math:

Video transcript

let's say we want to figure out what eight divided by four tenths is pause this video and try to figure it out on your own before we do it together all right now one way to approach this is to think about everything in terms of tenths and why tenths you ask well I just described the second number as four tenths so what would it be in terms of tenths well we know that we know that one whole is equal to ten tenths so eight holes is going to be equal to 80 tenths so I could write that down over here instead of eight I can write that as 80 tenths and I'm taking 80 tenths and I'm dividing that by divided by four tenths I'm just writing it out four tenths so if I have 80 of something and if I'm dividing it into groups of four of that something how many equal groups am I going to have well I'm gonna have 80 divided by four groups or 80 divided by four eight divided by four actually let me just write it down this is going to be equal to 80 over four or 80 divided by 4 and 8 divided by 4 is 2 so 80 divided by 4 is going to be equal to 20 so 8 divided by 4 tenths is equal to 20 another way that you could think about that is to rewrite 8 divided by 4 tenths as 8 over 4 tenths over 4 tenths and then if you wanted to rewrite this you could say hey can I multiply the numerator and the denominator by some quantity that'll get rid of the decimal in the denominator well I could multiply the denominator by 10 and if I don't want to change the value of the fraction I have to multiply the numerator by that same amount well that what does that get us well this is going to be equal to in the denominator right over here I'm just going to have a 4 so we got rid of the decimal and the numerator I am going to get 80 so once again we get 80 over 4 which is equal to 20 let's do another example but in this case we'll deal with hundredths so let's say we want to figure out what is 48 divided by 0.24 or 24 hundredths pause this video and try to figure that out alright well we can do something very similar this time we're dealing with hundreds so we could try to express everything in terms of hundredths so 48 is equal to how many hundredths well we know that 1 is equal to 100 hundredths undress so 48 so 48 is going to be equal to 48 times 100 hundreds and maybe I'll just write it like that or you might be able to say hey that's 48 hundred or 4,800 hundredths so let's just actually I'll write it that way this is going to be 4,800 hundreds hundreds divided by this is 24 hundredths 24 hundredths and so what's that going to be well same logic as we used up here if I have 4,800 of something or 4,800 of something and if I'm dividing it into equal groups of 24 of that something well I'm going to have four thousand eight hundred divided by 24 equal groups so this is going to be equal to 4,800 over 24 we could express 4,800 as of course 48 times 100 so this is equal to 48 times 100 over 24 and of course you could view this as the same thing as this is equal to 48 over 24 48 over 24 and many of you might have already done it in your head times 100 what's 48 divided by 24 well that is going to be equal to 2 so 2 times 100 is equal to 200 so this right over here is equal to 200 you could also do it in this type or do it the similar the way we did this where instead of expressing it out as words you could express it as 48 over 24 hundredths and instead of multiplying the numerator by 10:00 maybe you want to multiply it by something else to get whole numbers in both the numerator denominator think about that after this video and try to work it out that way as well