A car park has 41 spaces. Two spaces are taken. How many are left?
In this question, the car park has
41 spaces. If two spaces are taken, to
calculate how many spaces are left, we need to subtract the two spaces that are
taken from the 41 spaces in the car park. So we’re subtracting a one-digit
number from a two-digit number. We can model the number 41 using
four 10s blocks and a ones block. When we’re subtracting using the
column method, we always start with the ones first. We’ve got one in the ones place,
and we need to subtract two. We don’t have enough ones to
subtract from. So we need to take one of our tens,
leaving us with three 10s, and exchange it for 10 ones. Now we have 11 ones.
Now that we have enough ones, let’s
subtract in the ones place. 11 ones take away two ones leaves
us with nine ones. Now what we need to do is subtract
in the tens column. Because two is a one-digit number,
there’s nothing to subtract. We had four 10s. We exchanged one of our tens for 10
ones, which leaves us with three 10s. 41 subtract two equals 39.