Saturday, September 4th, 2010
If you have a function called ƒ, let’s call its inverse ƒ–1 (i.e. ƒ–1 is the inverse function of ƒ).
By definition, the property of ƒ–1 is that if ƒ(a)=b, then ƒ–1(b)=a. Wikipedia (http://en.wikipedia.org/wiki/Inverse_function) has a good example:

A function ƒ and its inverse ƒ–1. Because ƒ maps a to 3, the inverse ƒ–1 maps 3 back to a. In mathematics, if ƒ is a function from a set A to a set B, then an inverse function for ƒ is a function from B to A, with the property that a round trip from A to B to A (or from B to A to B) returns each element of the initial set to itself.
Monday, July 19th, 2010
Solution:
You can simply 12 – ( x + 3 ) +10 by rearranging the terms:
- 12 –x -3 +10
- 19-x
Saturday, July 17th, 2010
Here’s how you solve this type of question:
- Start with an equation like 3x + 5y = 15
- Move 3x to the other side, so 5y = 15 – 3x
- Divide both sides by 5, so y = 3 – x
- Another way of writing this is y = -.6x + 3, or y=mx = b, where m=-0.6 and b = 3
- If m = -0.6, that means that the slope =-0.6
Saturday, July 17th, 2010
Solution:
This is a well known “trick question”. It’s simply a series of squares with the digits reversed:
12 = 1 => 1
22 = 4 => 4
32 = 9 => 9
42 = 16 => 61
52 = 25 => 52
62 = 36 => 63
72 = 49 => 94
82 = 64 => 46
92 = 81 => 18
Saturday, July 17th, 2010
Here’s how you solve this type of question:
- The base of the 3D rectangle is in the shape of a 2D rectangle.
- Multiply the length of this 2D rectangle by its width to let the area
Saturday, July 17th, 2010
Solution:
The arithmetic mean is the average.
http://en.wikipedia.org/wiki/Arithmetic_mean
Saturday, July 17th, 2010
Solution:
Volume of wood is 72*54*48 = 186,624 cmcube; the mass would be 186,624 * 0.9 = 167,961.6 g.
Friday, July 16th, 2010
Solution:
If we let the age of the father be “F”, and the age of the son be “S”, then we know the following:
1. F = 3 x S
2. F+S=40
Therefore, F=3x(40-F)…so 4F=120.
Therefore, F=30 and S=10.