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- Multiplying or dividing by powers of 10
- If you want to multiply or divide some number by a power of ten, e.g. 13,3 * 100,13.34 * 10 = 133.413.34 * 1000 = 13340.0 = 13340.

Divisions are the inverse, so dividing by a power of ten is a shift of 1 to the left, e.g.13.34 / 10 = 1.33413.34 / 1000 = 0.001334.

Note that we added 0s to the left, because the shift was greater than the amount of decimal places to the left.

This strategy can be combined with other strategies, e.g.x * 50(x * 5) * 10,x*5,

- Multiplying a two digit number by 11
- This trick is very useful and yet simple to learn. Let's say you want to multiply 63 by 11. One way to
do this
is to split the calculation into
(63*10) + (63*1) = 630 + 63 = 693.6 + 3 = 9.63 * 11 = 6
**9**3.8 + 1 = 981 * 11 = 8**9**1.8 + 7 = 15.1+8 = 9.87 * 11 = 957.

- Adding numbers
- Everyone, and I mean literally everyone, learned to add numbers from right to left. The reasons for
this are
unknown to mankind. So I urge you to forget about that and start adding numbers from left to right. You
read numbers from left
to right, so why would you do anything different when calculating the number in question? You will
become a lot quicker, trust me.
Let's do some examples. First we look at 68 + 25. We start with
68 + 20 = 88,88 + 5 = 93.873 + 100 = 973,973 + 30 = 1003,1003 + 8 = 1011.

- Squarring two digit numbers.
- First of all everyone should know squares up to 25 (or at least 20) by hard. This won't take you more
than 5 minutes to master, no worries. However, here is a neat to tip to square two digit numbers.
Let's look at 15 * 15. You should know that this is equal to 225, but let's say you did forget it (shame
on you).
What are numbers in the near distance of 15, which are easy to multiply? Clearly, 20 and 10 are really
nice. Even better,
they have the same 'distance' from 15 (namely 5). So what to do now? Simple:
15 * 15 = 20 * 10 + 5 * 5 = 225.14 * 14 = 18 * 10 + 4 * 4 = 196.42*42 = 44 * 40 + 2*2 = 1760 + 4 = 1764.57 * 57 = 60 * 54 + 3 * 3 = 3000 + 240 + 9 = 3249.16 * 14 = 15 * 15 - 1 * 1 = 224.19 * 15 = 17 * 17 - 2 * 2 = 285.