Number Properties

Whole numbers are natural nos Union Zero.

Statistics

By definition, the median of the combined set (A) must be any value at or between the medians of the two smaller sets (B and C).

Look at the link for example:http://www.beatthegmat.com/manhattan-gmat-700-challenge-problem-august-7-2006-t357.html

Co-Ordinate Geometry

If the line has a negative slope, it passes through one of the following: II,I,IV ; II, III, IV; II, IV.

Alligation

The proportion needed of each starting percentage is the positive difference between the other 2 percentages.

Refer to the following link for examples : http://www.beatthegmat.com/mixture-t76266.html

Mean & Standard Deviation

1) If we multiply each element of a set by a common factor/ (or increase/decrease each element by fixed %) / ( increase/decrease each element by the same amount then):

New Mean or New SD = Old Mean or Old SD * common factor.

New Mean or New SD = Old Mean or old SD * (1+% increase/decrease)

New Mean or New SD = Old Mean or Old SD + increase/decrease in amount.