Fourth Grade - Lesson 4.5 Estimating Quotients Using Compatible Numbers
May 26, 2015
Hi, my name is Jamie couture from PS1 on one school in Brooklyn. Today I'm going to show you how you can use compatible numbers to estimate the oceans. What are compatible numbers? Compatible numbers are numbers that are easy to compute mentally. So simple facts that you can still numbers that you can do in your head. Let's unlock the problem. A horse's heart beats 132 times in three minutes above how many times does it be in one minute? So in order to solve this problem, we would have to divide a 132 divided by three because the question is asked in a town many times as if the in one minute. So we need to figure that out. A clue word about lets us know we need to estimate. They're not looking for the exact answer. They're looking for an estimate. So let's do that using compatible numbers. And again, compatible numbers are numbers that you that are closest to the exact number they give you that are easy to divide in your head. So using your basic facts of 132 divided by three, think of what number that's close to a 132, that three can go into easily. Three can not go into 13 evenly, but what number is 13 closest to? 12. So if we would replace a 132 to a 120, this number is compatible because three can go into one 20 evenly, and it's close to a 132. So the simple fact is 12 divided by three, which is a 120, really, divided by three. Another close fact, if you think of the three times table, is 15. So if we change a 132 into a 150, that can also be compatible. So which one do we use? We use 120, because 120 is closest to one 32. One 50 is a bit too high. So using that, we are now going to divide to use in place value. So 120 is actually equal to 12. 12 divided by three equals four. So four tens is like saying four times ten, which is equal to 40. So I'll final answer would be a horse's heartbeat about 40 times a minute. Again, this is an estimate. Let's try another example. Let's use compatible numbers to find two estimates that the quotient is between. Let's use the number 1382 divided by 5. Find the two numbers closest to 1000. 382 that 5 can go into easily. So I always look at the first two numbers. Can find go into 13 now, but what number the 5 times table below and above can it go into? So below 13 would be turned, correct. So we would do ten divided by 5. As an easy basic fact, which really translates into this number 1000 divided by 5. Or a mix number closest to 13 would be 15 and 5 can go into. So we do 1500 of this number goes up to a thousand. Now we decide which ones closest to 1382. 1000 or this 1500. So the closest one would be 1500. So let's divide that. This is your compatible number. Using a basic division fact. 1500 divided by 5 and 5 goes into 15 three times, which is 300. So three times 100 gives you 300. So your answer is 300s. Thank you for joining me today. Have a great day.