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### Course: Early math review > Unit 7

Lesson 3: Comparing and estimating length# Estimating lengths

Sal estimates the length of an object when given the length of another object.

## Want to join the conversation?

- Why do we estimate instead of doing the problem?(27 votes)
- Good question. There are loads of reasons! Here are some -

1. Estimating can be much quicker than solving the actual problem.

2. We don't always mind about having exactly the right number, we just need to know it roughly.

3. Sometimes we don't have everything we need to solve the problem 'properly' (e.g. we might not have a ruler to hand)(53 votes)

- What does Estimate mean?(3 votes)
- When you estimate, you roughly find out a value. It's not an exact answer, but instead a number close to the actual value or a range that has the value in it. You can estimate when you're not sure of the actual answer, like Sal did in the video.(19 votes)

- What must you do if your estimates are incorrect or not even close to your actual answer?(9 votes)
- Think about the situation again with a clear mind and you will be able to find your mistake and correct it .

Good Luck !!(7 votes)

## Video transcript

- [Voiceover] Lets get some
practice estimating lengths. So they tell us this line is one inch. So that distance right
over there is one inch. About how long is a toy car? Well, this is one of those
lines that they just did so that's one inch, but let's just see how many of those we need to go the whole length of the car. So if I were to draw another one that's about to that, and I'm estimating, it's not exact, that would be two inches. That's one inch, that's two inches. Then that would be three inches. And then that would be four inches. So it looks like the car
is about four inches. Let's do another one of these estimating length problems. So I have a picture of two sunflowers right over here, and they tell us that this first sunflower
is 40 centimeters tall. About how long is this
second sunflower going to be? Lets think about it. If this entire distance, if this entire height is 40 centimeters. And this sunflower, if
you look at its height, I'll draw a dotted line here. It looks like it's about half of the height of the taller sunflower. So what is half of 40 going to be? Well, 40 is four tens. Half of four tens is going to be two tens. So this looks like it's
about 20 centimeters, let me write it this way, this looks like it's about 20 centimeters. Another way to think about it is if this whole thing is 40
centimeters then half would be 20, then this would be 10 centimeters. Let me write this, this
would be 10 centimeters. This would be 20 centimeters. Then this would be 30 centimeters. Then this would be 40 centimeters. So we already saw that the
sunflower is 40 centimeters tall. And then this one would be half of that. It would be 20 centimeters tall.