At the start of June, there were 1793 toy cars in a shop. During June, 8728 more cars were delivered and 9473 toy cars were sold. How many toy cars were left in the shop at the end of June?
We can think of this problem as being on initial timeline. And a timeline takes us through the steps that we need to do to solve the
problem. At the start of the month, the shop has 1793 toy cars. Then during the month, we’re told two different things happen.
Firstly, we’re told 8728 more cars were delivered. This is a lot more than they already had. Perhaps, they ordered them in from the factory ready for all the sales that we’re
going to have. To find 8728 more than a number, we need to add it.
The second thing that happens during June: we’re told that 9473 toy cars were
sold. In other words, they’re not in the shop anymore. The number of toy cars that were in the shop has been reduced by 9473; we need to
take it away. And the final sentence in the problem asks us about the end of the month: how many
toy cars are left in the shop at the end of June?
So by imagining this timeline, we can see the two steps that we need to do to find
the answer. First, we need to take the number of toy cars that there were in the shop at the
start of June. And in step one, we need to add the number of cars that were delivered: three plus
eight equals 11.
So we can write one in the ones column and exchange 10 ones for one ten. Nine tens plus two tens equals 11 tens plus the one ten underneath equals 12
tens. We can write two of those tens in the tens column and exchange 10 tens for 100. Seven hundreds plus seven hundreds plus the one that we exchanged equals 15 hundreds,
which we know is the same as 1500.
Finally, one thousand plus eight thousand plus the one thousand that we exchanged
equals 10 thousand. And so after they had the delivery, the shop had 10521 cars. But of course, we know something else happened in June. 9473 of those cars were sold. And so, step two is to subtract 9473.
Let’s use column subtraction. We can’t take away three from one. But we can shuffle around the number a little bit and partition it in a different
way. Let’s take one ten and exchange it for 10 ones. Instead of two tens, we now have one ten. And instead of one one, we now have 11 ones. Now, we can subtract three. 11 take away three equals eight.
We can’t subtract seven tens from one ten as seven is greater than one. So we need to exchange again. This time, we can exchange one hundred for 10 tens. Instead of five hundreds, we now have four hundreds. And instead of one ten, we now have 11 tens. 11 tens take away seven tens leaves us with four tens. Four hundreds take away four hundreds leaves us with nothing.
We can probably see what the answer to the last column is going to be. But let’s exchange anyway just to show what we’re doing. We’ll exchange one lot of ten thousand and change it for 10 lots of one thousand. 10 thousand take away nine thousand leaves us with one thousand. And so, we found the number of toy cars that they were left at the end of June.
We found that there were two steps to this problem and we used written methods for
both. We started with the number of cars that they were to begin with. And the first thing that we did was to add the number of cars that were
delivered. This gave us the total amount of cars that were in the shop during June. But we knew a lot of cars were sold. So in step two, we subtracted the number of cars that the shop sold.
And so, the number of toy cars that were left in the shop at the end of June was