Multiplying 3-digit by 2-digit numbers: Error analysis | Grade 5 (TX TEKS) | Khan Academy

- [Instructor] So we have a situation here

where someone is attempting
to multiply 586 times 43,

and what we wanna do
together is figure out

if they did this correctly or
whether they made a mistake.

And if they made a mistake,

what step did they make a mistake on?

And actually, why don't
you pause this video

and have a go at this on your own

before we work through this together.

All right, now let's work
through this together.

So let's start at the beginning.

Here we have 3 times 6 is 18,

so you put the 8 here, regroup the 1.

That all looks good right now.

Then you have 3 times 8 is 24,

plus that 1 that we just regrouped is 25.

Put the 5 here, regroup the
2. All looking good so far.

3 times 5 is 15, plus 2 is 17.

Wrote the 17 here. So step
one all looks good to me.

Now let's look at. We're now now going to.

Now let's move on to the
4, which is really a 40,

so we're gonna put a zero right over here.

And then we're gonna say 4 times 6 is 24.

Put the 4 here and regroup the 2.

4 times 8 is 32, plus 2 is 34,

put the 4, regroup the 3.

4 times 5 is 20, plus the 3 is 23.

So it looks like a mistake
was made in step two.

And of course step three
is gonna break down

because they forgot to put
the 3 right over there.

So definitely a mistake, and
the mistake is in step two.