THE 7 × TABLE
In Pathmatics we do not duplicate multiplication facts that have already been mastered.
And if you are using this book correctly, your learners have already mastered 0 × 7 = 0, 1 × 7 = 7, 10 × 7, 9 × 7, and 8 × 7.
That leaves 2 × 7, 3 × 7, 4 × 7, 5 × 7, 6 × 7 and 7 × 7.
Logic tells us that when multiplying any of these digits times to seven, the number in the tens place must be less than the smaller digit. But, with 7 × 7, neither digit is smaller. Would we do then?
This is the only time when the number in the tens place will ever be more than two. When multiplying two identical digits (3 × 3, 4 × 4, 5 × 5, 6 × 6, 7 × 7) the tens place will be three less than either digit.
So, 7 × 7 will be forty-something.
The pattern for the 7 × table is:
“7-Up, double up.”
We say “7-Up” because it is the 7 × table.
We say “double up” because you double the standing fingers on any incomplete hand (any hand that has less than all five fingers raised).
But, when representing seven on our hands and fingers, there are only two standing fingers on the incomplete hand. If you double them, you get four, not nine. And yet, we know that 7 × 7 = 49, so what gives?
Unfortunately, when it comes to the middle five digits (3, 4, 5, 6, and 7) our patterns for the units place only work when multiplying times even digits. To make them work with odd digits, we have to apply one more step, which we call “modifiving the results.”
To modifive a result, you reduce it by five. However, if the result is too small to be reduced by five, then you increase it by five.
Since 7 is an odd digit, we need to modifive the result for the units place. After doubling the two standing fingers we have four -- too small to subtract five -- so we add five instead and get nine, exactly what we needed.
This process is too complicated for our taste, so we make an exception here and have our clients learn this multiplication fact through some other approach.
Now, we are left with 2 × 7, 3 × 7, 4 × 7, 5 × 7, and 6 × 7.
Logic tells us that when multiplying any of these digits times to seven, the number in the tens place must be less than the smaller digit, but how much less?
Well, in all but the first two cases, it will be two less, so we will postpone 2 × 7 and 3 × 7 until we get to the 2 × table and 3 × table respectively.
That leaves us with 4 × 7, 5 × 7, 6 × 7 and 7 × 7.
The 5 × table is so easy that we will postpone 5 × 7 until then as well.
Now, all we have is 4 × 7, and 6 × 7.
In both cases, the number in the tens place is two less than the smaller digit. That means that 4 × 7 = twenty-something and 6 × 7 = forty-something.
Both for and six art even digits, so our strategy for the units place will work without having to modifive the results.
Remember our strategy is “7-Up, double up.”
In representing four on our hands and fingers, we have four fingers standing. When we double them, we get eight, so . . .
4 × 7 = 28
In representing six on our hands and fingers, we have one finger standing. When we double it, we get two, so . . .
6 × 7 = 42
In this chapter, the following multiplication facts . . .
7 × 7 = 49
6 × 7 = 42
4 × 7 = 28
. . . are the only ones that need to be mastered. So, let’s go on to the 6 × times table.