Video Transcript
Sophia is subtracting by making
10. 13 subtract five equals what? Which calculation should she do
first? 13 take away two equals 11 or 13
take away three equals 10. And then, which calculation should
she do next? 10 take away two equals eight or 10
plus two equals eight.
And maybe you’ve noticed one of
these calculations doesn’t make sense, but let’s go through the question from the
start and find out what Sophia is doing here. We’re told that she’s subtracting
by making 10. And we can see from the picture the
two numbers that Sophia’s subtracting. She’s trying to find the answer to
13 take away five.
Now, she could find the answer just
by starting with the number 13 and counting back five. But we’re told that she wants to
find the answer by making 10. First, she can take away part of
the number five to get to 10. And then, she can take away the
rest of the number five from 10 because subtracting to and from 10 is quite quick to
do.
Here are 13 counters. And we can see from the diagram
that Sophia has split up the five that she wants to take away into two jumps. First, she takes away three. As we’ve said already, we know why
she does this; she wants to make 10. She knows that 13 take away three
equals 10. So, we know the calculation that
she needs to do first is 13 subtract three equals 10.
Now, Sofia knows that three and two
go together to make five. She’s already taken away three out
of five. Now, she needs to just subtract the
remaining two. And because she’s made 10, she
takes away two from 10, which is very quick to do. Now, if we look carefully to our
possible answers, only one of them makes sense. 10 plus two doesn’t make eight.
But let’s think about how Sophia
knows that 10 take away two equals eight. Well, she knows that two and eight
go together to make 10. She can subtract from 10 really
quickly. And so, the second calculation she
needs to do is 10 subtract two equals eight.
Sophia found the answer to 13
subtract five by splitting up five into three and then two. The calculation she should do first
is 13 take away three equals 10. And her next calculation should be
10 take away two equals eight.
