Exam2win.com|Aptitude Fundamental Formulaes

Formulae

Numbers

A number is divisible by 2 if the last digit is 0, 2, 4, 6 or 8.
A number is divisible by 3 if the sum of the digits is divisible by 3.
A number is divisible by 4 if the number formed by the last two digits is divisible by 4.
A number is divisible by 5 if the last digit is either 0 or 5.
A number is divisible by 6 if it is divisible by 2 AND it is divisible by 3.
A number is divisible by 8 if the number formed by the last three digits is divisible by 8.
A number is divisible by 9 if the sum of the digits is divisible by 9.
A number is divisible by 10 if the last digit is 0.

Ratio & Proportion

The equality of two ratios is called a proportion. If a : b = c : d, we write a : b :: c : d and we say that a, b, c, d are in proportion. In a proportion, the first and fourth terms are known as extremes, while the second and third are known as means.
Product of extremes = Product of means
Mean proportion between a and b is
The compounded ratio of the ratios (a : b), (c : d), (e : f) is (ace : bdf)
a2 : b2 is a duplicate ratio of a : b
a3 : b3 is a triplicate ratio of a : b
a1/3 : b1/3 is a sub-triplicate ratio of a : b
If a / b = c / d, then, (a + b) / b = (c + d) / d, which is called the componendo.
If a / b = c / d, then, (a - b) / b = (c - d) / d, which is called the dividendo.
If a / b = c / d, then, (a + b) / (a - b) = (c + d) / (c - d), which is called the componendo & dividendo.
Variation: We say that x is directly proportional to y if x = ky for some constant k and we write, x a y.
Also, we say that x is inversely proportional to y if x = k / y for some constant k and we write x a 1 / y.

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