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Data Sufficiency Tips
1. Most data sufficiency questions involve numbers, integers, factors, divisors and multiples.
a. You need to understand what an integer is. Note that integers can be positive or negative.
b. You need to understand what a prime number is. Note that 2 is the only prime number that is even. Do not make the assumption that all prime numbers are odd because 2 is an exception which should be taken into account when answering the question.
c. You need to understand what a factor is and what a multiple is. Also, for this type of problems, knowing the divisibility rules for 2 thru 9 would also help.
d. Note that if x is divisible by 3 and y is also divisible by 3, then any linear combination of x and y such as x+y, x-y, or 2x+3y etc are all divisible by 3.
2. Always identify the problem domain and write it down.
For example, if the problem states that x is a positive integer, note down that x > 0.
If the problem statements that x is an even integer, note that x can be positive or negative, and hence, x = 2,4,6,8â€¦etc or -2,-4,-6,-8..etc
3. For problems involving square roots, always consider both positive and negative square root unless otherwise stated.
For example, if x ^2 = 49, note that x can be 7 or -7.
However, if the problem states that x is a positive integer and x^2 = 49, then x = 7.
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