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### Course: 4th grade > Unit 3

Lesson 4: Estimate products# Estimating with multiplication

Sal estimates to find reasonable products to 1-digit by 2, 3, and 4-digit multiplication expressions.

## Want to join the conversation?

- Question: How do you know what number is a friendly number or not?

And how do you know when you are supposed to round a single-digit or ten-digit number up or down?

It looks like sometimes when estimating what to round up or down you sometimes have to round both numbers down like 16 to 15 and 1111 to 1000. I have trouble knowing what to round up or down if it's not asking for a friendly number.

This is a similar problem I had when estimating was first introduced in the 3rd-grade segments of Khan Academy. Those questions weren't fully mentioned besides rounding by 10s 100s, and 1000s.(17 votes)- You round up if the number is five or higher you round down if lower than five(4 votes)

- What does the squiggly equal sign mean.And why(8 votes)
- the squiggly equal sign means that the following phrase is approximately the right sum

for example 146+100 equals almost* 250

* I used "equals almost" insted of the squiggly equal sign, but thay mean the same thing

so the sum of this problem is

squiggly equal sign 250(1 vote)

- what kind of sign is this ~(8 votes)
- It means that an answer is close to the right answer, so it not exactly right.(5 votes)

- What is the squiggly equal sine(2 votes)
- it means around (estimated)(3 votes)

- I think this video is so helpful! Befor on this assignment i got only 25%, but when I watched this video I got 95%!💯(3 votes)
- That's great. So happy to see you learn :)(1 vote)

- In the Estimate Products Lesson do you estimate the first or second number? I tried estimating the largest number but got it wrong when I tried!(2 votes)
- I am so confused with the video(2 votes)
- Well all you do is multiply to find the product. Then you find the awnser that is closer to the product. for example. 189*2 is 387. and the closes number to it is 400 if it were the smalles number in the awnsers. Hope this helped.(0 votes)

- Will we have these questons(1 vote)
- why does estimates have to go with the digits that are gonna to multiply instead of the answer?(1 vote)
- I do not get it how does that wherk.(0 votes)

## Video transcript

- [Instructor] In this video,
we're gonna get a little bit of practice estimating
with multiplication. So over here it says question
mark is, and then you have this squiggly equal sign. And so you can view that
squiggly equal sign as being what does this roughly equal to? It doesn't have to be exactly right. So what is roughly equal to 58 times six? And so which of these
choices would you pick? Pause the video and see
if you can answer that. So once again, we don't have
to get this exactly we just need to estimate what 58 times six is. And the way that I would
tackle it is hey, can I rewrite 58 as a number that is easy
to multiply by six or easy to multiply in general? And the easiest thing I can think of is 58 is awfully close to 60. So if you say that that is
close to 60 if we're just estimating it, well what
would 60 times six be? Well 60 times six is the same
thing as, actually let me just write it this way. You can view 60 times six
as six times 10 times six, which you could also view
as six times six times 10. And what's six times six? That's 36. And then 36 times 10 is 360. So I would go with that
choice right over there. Notice, these other choices
aren't anywhere close to that so we feel pretty good
about our estimation. Let's do another example. So here we're asked
what's three times 2,890? What's that roughly equal to? How would you estimate this? Pause the video and see if
you can figure that out. Alright, so 2,890 is not an
easy thing to maybe multiply in our heads, but I can say
hey, that's kinda close to 3,000 so I'm gonna say that this
is going to be approximately equal to, or roughly equal
to, three times 3,000. Now what's three times three? That's nine. So what's three times 3,000? We'll it's gonna be nine thousands. So it would be this
choice right over here. If what I just did was a little
bit confusing, you can view three times 3,000 as three
times three times 1,000. This part right over there is 3,000. Three times three is the nine, and you have nine thousands, 9,000. Let's do one more example. This is going to involve
fairly large numbers. So what is, if you had to
estimate 5,111 times nine. Which of these would you pick? Pause the video and answer that. Alright, so I would view
this, this is roughly, I would estimate it, as 5,000 times 9. And so 5,000 times nine, that's
the same thing as five times 1,000 times nine, which is
the same thing as five times nine times 1,000. Five times nine is 45, so
it's gonna be 45 thousands, or 45,000 which is this
choice right over there.