Video Transcript
Complete: 10 times four times seven
equals 10 times what?
This question relies on us
understanding that we can multiply numbers in different orders and still get the
same answer. For instance, if we want to work
out the answer to 10 times four times seven, one way to find the answer might be to
work out 10 times four first and then to multiply that answer by seven. Another answer might be to work out
four times seven first and then times the answer by 10. Or we could even really juggle the
numbers around and multiply 10 by seven first and then multiply that answer by
four. However we do it, we’re always
going to get the same answer.
So let’s think about the first
multiplication to start with. What does 10 multiplied by four
multiplied by seven mean? Well, if we worked out this in
order, then we’d calculate 10 multiplied by four first and then multiply that by
seven. Let’s use this rectangle to
represent the multiplication 10 times four. So if we work out 10 times four
times seven, this means we need seven of these rectangles. There are two, three, four, five,
six, seven. This diagram represents the first
calculation, 10 multiplied by four seven times.
Now let’s think about the second
part of our number sentence. 10 multiplied by what? In the same way as we’ve just done,
we can draw another rectangle to represent this multiplication. The height of our rectangle is
going to be worth 10 again. And we need the length to be
exactly the same as the length of the other rectangle. The length of the rectangle is the
same as seven fours. In other words, to find out our
missing number, what we have to do is to calculate the four times seven part of our
multiplication first.
Let’s count in fours seven times to
find out what it’s worth. Four, eight, 12, 16, 20, 24, and
28. The missing number is 28. All we’ve done is multiply the four
times seven part of the calculation first. This leaves us with 10 times 28 to
find the overall answer. 10 times four times seven equals 10
times 28.
