Question Video: Estimating the Result of Multiplying Fractions by Whole Numbers

Video Transcript

Estimate four-fifths of nine. And we ’ ve got five possible answers to choose from : two, 12, eight, three, and four. This question is asking us to estimate the measure of four-fifths of nine. Why international relations and security network ’ metric ton it asking us to calculate the value of four-fifths of nine ? Well, normally, if we ’ rhenium being asked to find four-fifths of a number, we start by dividing that count by five. This will give us the value of one-fifth. And if we know what one-fifth is worth, we then multiply it by four to find the value of four-fifths. But the trouble is nine international relations and security network ’ t a multiple of five. And indeed, if we tried to do the first step and divide nine by five we ’ ra not going to get a whole phone number as an answer. And thus, this is why the question is asking us to estimate the respect of four-fifths of nine. There are two ways we can estimate the answer. The first base way is to use a little bit of number sense. We know already and we can see from the barricade model that four-fifths is closely one unharmed. We can ask ourselves which of the five numbers is very closely nine. well, immediately, we can see one number that it decidedly international relations and security network ’ deoxythymidine monophosphate. It ’ s impossible for four-fifths of a number to be a number greater than that number. So the suffice can ’ triiodothyronine be 12. And out of the remaining numbers, it looks like the numeral eight might be the numeral we ’ re looking for. It ’ randomness very close to nine. But it ’ s not quite one unharmed. Another method acting we could use to estimate four-fifths of nine is to round nine to a issue that ’ second easier to deal with. Nine is very close to 10. Let ’ s see what happens if we try to find four-fifths of 10. It should give us an answer fairly close to four-fifths of nine. Remember how we described we ’ re going to find the answer ? First, we divide the number by five. And we said the reason we were going to do this was to help us to find one-fifth of the total. 10 divided by five equals two. So one-fifth of 10 is two. We immediately need to multiply this by the number of fifths we need, which is four. And this will give us the value of four-fifths.

Two multiplied by four or four multiplied by two equals eight. And so, four-fifths of 10 is eight. We ’ five hundred expect four-fifths of nine to be less than eight, probably between seven and eight. But that ’ s not one of the choices that we have. So out of our number of five numbers, the best number to estimate is the issue eight. We used two methods to find the answer. The first method acting we used was to use some numeral sense. We knew that four-fifths was very about one whole. And therefore, we look for a phone number that was very near to one unharmed if we were thinking about the number nine. The number eight was very close to nine. Our irregular method which we used to check our estimate with was to find four-fifths of a number that was easier to work with. Nine is very close to 10. And so, we calculated four-fifths of 10, which we found was eight. Out of the numbers we ’ re given, our best estimate for four-fifths of nine is eight .

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