### Video Transcript

A group of elephants drink 982
liters of water each day. How many days will 4910 liters of
water last?

In this problem, we’re given an
amount of water, 4910 liters. And we’re told that a group of
elephants drink 982 liters every day. We need to find out how many days
this large amount, 4910 liters, will last. So in other words, we need to
divide 4910 by 982. How many lots of 982 are there in
4910?

This is an interesting question
cause we might normally say let’s use long division. But we can’t find the number of
982s in four, 49, or even if we look at the first three digits of our number,
491. We have to just consider the whole
number. How many 982s are there in
4910? We can’t do it bit by bit. So how could we find the answer if
we don’t know our 982 times table?

Well, one method we could use is to
start with 4910 and then use repeated subtraction, taking away more and more lots of
982 until we get to zero. That way, we could find out how
many 982s there are in 4910.

Another method we could use is
reasoning. Let’s use this method here now. Which multiplication fact do we
know about 982 straight away without really thinking about it? Well, we can say that 10 lots of
982 are 9820. The digits shift one place to the
left. Now compare this answer, 9820, by
the number that we need to divide, 4910. What do we notice?

We know that half of 9000 is
4500. So could we say that 4910 might be
around about half of 9820? It could be. It might be a good idea to work out
what five times 982 is worth. To do this, we can use short
multiplication. And even if we’re wrong, we could
adjust our answer to find out what four lots of 982 or maybe six lots of 982
are.

But let’s start with five lots to
begin with, 982 multiplied by five. Two times five equals 10. This is looking promising. The number that we need to get
close to, 4910, ends in a zero. Eight times five equals 40. We’ve got one 10 underneath. So that gives us 41 tens. Looks like we might have found the
right answer. We have a one in the tens place,
which is what we needed. Now nine times five equals 45. So nine hundreds times five is 45
hundreds. We’ve got four hundreds
underneath. So this takes us to 49 hundreds,
4910.

We estimated that there might be
five lots of 982 in 4910. And so we worked out the
multiplication. And we were right. There was. If a group of elephants drink 982
liters of water each day, then we know that 4910 liters of water will last five
days.