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Comparing decimals word problems

CCSS.Math: ,

Video transcript

al is comparing two recipes for homemade bread the recipe for white bread calls for 4/10 of a kilogram of flour the recipe for whole-wheat bread calls for 385 thousandth of a kilogram of flour which bread takes less flour so the white bread calls for 4/10 of a kilogram while the recipe for whole wheat bread calls for 0.385 kilograms or 300 385 thousandths of a kilogram now the way I wrote it is important you always want to line up the decimals when you are comparing because you want to compare numbers in the same place value and this is an interesting example of even though the number down here has more digits it doesn't mean that it's necessarily a larger number what we want to do when we compare numbers and this is true whether we're dealing with decimals or not is we start in the largest place value we could start in the ones place both of these have zero ones then we go one place value down we go to the tenths place the white bread it requires four tenths of flour while in the whole-wheat bread we only have three tenths of flour so we can stop right there this has more tense than this does it doesn't matter that this has more hundreds and thousands those are less significant they don't add up to as much as that as what we're dealing with when we look just like when we look just at the tenths place so because 4 is greater than 3 and we're in the tenths place we know that white bread takes more flour we have to be very careful they said which bread takes less flour so it's going to be whole-wheat bread three is less than four let's do another one of these a group of fifth graders kept track of the number of hours they spent working on their science project alright put the students in order from the least to greatest amount of time spent the student with the least amount of time should be at the top of the list so pause this video and see if you can do this and this is actually a screenshot from the Khan Academy exercise if you're doing the kind Kaddi exercise you actually be able to click on these and move them around let's compare them so as I mentioned in the last example when you're comparing numbers it's good to line up the place values so let's do that so adam is 5.5 aviv is 5 and jenny is five point one seven so once again start at the largest place value start at the ones they all have exactly five ones so that we move to the next place value in this case we're going to go to the tenths place so when we look at the tenths place interesting things are going on aviv has no tents it's a blank here but you could view this as five point zero so vivre has the fewest tenths then comes Jenny with only one tenth and then Adam has five tenths so that tells us enough so we can order the three we don't even have to look at the hundreds place because the tenths here are different so the least number of tenths is Aviv so that's going to be a vivre is the least they all have the same number of ones but Aviv's has the least tenths then comes Jenny Jenny once again they all have the same number of ones but then Jenny has less tenth than Adam and then comes Adam Adam has the most Adam has the most tense it doesn't matter that Jenny also has seven hundredths notice you could do this as 1700s which is going to be less than five tenths which could also be viewed as fifty hundredths so the general way to think about it start at the most significant the largest place value compared if things are equal go to the next place value when things are different then you have enough information to start ordering them