 Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫  π  -¹ ² ³ °

You are not logged in.

## #1 2020-06-29 06:04:47

pi_cubed
Member
From: A rhombicosidodecahedron
Registered: 2020-06-22
Posts: 42
Website

### Do mental multiplication quickly

This is more of an algorithim, but here is how you can do any number times a one digit number quickly.

``````167859*7
1*7
6*7
7*7
8*7
5*7
9*7
|
\/
7
42
49
56
35
63
'''To put the numbers together just put them next to each other e.g 12*3 => 1*3 and 2*3 => 3 and 6 => 36. If the result has a 2 digit number then add the tens place from the 2 digit number to the next number left or above's ones place.'''``````

Credit to Abhishek V. R. for this method of doing mental multiplication.
Edit: I may not have written the part about putting the numbers together right. Please google "ofpad mental multiplication left to right" for the correct method.

Last edited by pi_cubed (2020-06-29 06:13:15)

e to the i pi plus 1 is zero -Leonhard Euler | a squared plus b squared equals c squared -Pythagoras | Energy equals mass times the speed of light squared -Albert Einstein | i² = -1 |
X Y X' Y' ≠ X' Y' X Y = Y' X' Y X -Me talking about some random group theory relationships

Offline