Estimating the product of two, 2-digit numbers. Created by Sal Khan.
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- what is kilometers?(29 votes)
- at0:05what is rounding?(5 votes)
- Rounding is a type of estimating. 42 is close to 40 = 4 tens. 29 is close to 30 = 3 tens.
Do 4 tens times 3 tens in your head.
4 * 3 = 12 and 'tens place' times 'tens place' = 'hundreds place'
So our estimate is 12 hundred = 1200(15 votes)
- SO i get it a little bit but do you always multiply if so it would be a lot easier and also why do you round. PLEASE ANSWER I'm stuck(7 votes)
- no not always. it depends on what you need to find out, and as far as rounding goes, it's just a way to estimate (guess) when you don't need an exact anwser.(7 votes)
- Couldn't you just round the answer after you got the exact answer?(5 votes)
- You could but the idea is that with rounding the problem become much easier and you may find you can do it in your head.
Sometime we don't always need an exact answer but a good idea, this is why we use rounding.(9 votes)
- What is the point of estimating if its not even the right answer? even if its close, one little mistake will change the whole answer. Do they do it because it is faster?(3 votes)
- How do you do this i need help(2 votes)
A ticket agent sells 42 tickets to a play. The tickets cost $29 each. Use rounding to estimate the total dollars taken in from the sale of the tickets. Now if we wanted the exact number, we could say 42 times 29, and we could work out the multiplication, but they essentially want us to be able to do it in our head. We want to round the numbers first and then multiply. So if we want to round, and really we just have two places here, so if we're going to round anything, it's going to be to the nearest ten because that's the largest place we have. So if we round 42 to the nearest ten-- we've done this drill many times-- 2 in the ones place is the less than 5, so we're going to round down. The nearest ten is 40. We're going to round down to 40. 29, if we round to the nearest ten, 9 in the ones place is greater than or equal to 5, so we round up. The nearest ten is 30. And another way to think about it. Just say, well, you know, 42, that's pretty close to 40. 29 is pretty close to 30. Those are literally the nearest multiples of ten that I can figure out, so now I can multiply. And here, once again, we can use-- you could call it a trick, but hopefully, you understand why it works. But 30 times 40, instead of you saying, well, this is going to be the same thing as 3 times 4, but we're going to put two zeroes at the end of it. 30 times 40 is the same thing as 3 times 4 with two zeroes, so let's do that. So you have 3 times 4 is 12, which we know, and then we have two zeroes. We got that zero, so let's stick that zero there, and then we got that blue zero there, so let's put that over there. So they're going to have roughly $1,200 taken it from sales of the tickets. That is our estimate.