If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains ***.kastatic.org** and ***.kasandbox.org** are unblocked.

Main content

Current time:0:00Total duration:3:09

CCSS Math: 4.NBT.B.5

- [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.