|
While trying to find
a rhyme or reason for multiplying 7s, i came up with the following
method. I've looked around on the web to see if anyone else
mentions this pattern, but i haven't found it anywhere.
When
multiplying 7 by any number divisible by 3, a pattern emerges
that can help kids solve the equations.
Let's
start with 7 x 3 = 21. Look at it this way:
7
x 3
=
2 1
See
how the numbers are counting down? Now let's look at 7 x 6.
The number 6 is basically just 3 + 3, right? Two 3s. So instead
of counting down by 1s, you count down by 2s. Like so...
7
x 6=
4 2
See?
Simple, right? Next try 7 x 9. Nine is 3 + 3 + 3 or three
3s. So now we count by 3s.
7
x 9=
6 3
And
this pattern works for all numbers divisible by 3. Let's do
one randomly. How about 7
x 18
=
12 6
7
x 24
=
16 8
Of
course, once you get to 7 x 30, you have to start recognizing
the tens and ones columns. At that point, you might want to
switch to either the lattice method or Chinese multiplication.
I
hope this helps anyone struggling with those nasty 7s!
|
