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CCSS Math: 4.NBT.A.2

We have 4,5000 equals 3
thousands plus how many hundreds, question
mark hundreds? So let's write this
left-hand side, but I'm going to
write it out in terms of thousands and hundreds. So I'll write the
thousands in orange. So this is equal to
4 thousands, which is the same thing as just 4,000,
plus 500, which you could also view as 5 hundreds. So this is the left-hand side. Now let's look at
the right-hand side. We have 3 thousands. So it's 3 thousands. Now let's not even
look at this right now. Let's just think
about what do we have to add to this
right-hand side in order to get the
same thing that we have on the left-hand side? Well, if you compare
the 3,000 and the 4,000, you see you have an
extra 1,000 over here. So let's add an extra
1,000 on the right. So we're going to
add one extra 1,000. And now we just have
3,000 plus 1,000. This makes it the 4,000. But then, of course, we
also need another 500. So we're going to need
plus a 500 right over here. So in order for these
two things to be equal, we need to say 4,000 plus 500
is equal to 3,000 plus 1,500. Now, the way they've set
this up, we need to express-- so it almost looks the same. On the left-hand
side, this is 4,500. So this right over here, this
is the same thing as 4,500. This is this right over here. And on the right-hand
side, we have 3 thousands. So that's this right over here. That's the 3 thousands. And then we just need to
express this as hundreds. So 1,500, this is the
same thing as 15 hundreds. So let's rewrite everything. We can rewrite this
as saying 4,500, just to get the exact same form
that they wrote it over there. So we could write 4,500 is
equal to 3 thousands plus-- now we have to just write
this in terms of hundreds. Well, This is 15 hundreds. Literally, if you
took 15 times 100, it's going to be equal to 1,500. So this could be viewed as 15
hundreds, so plus 15 hundreds. So in this situation, the
question mark is equal to 15.