Practice GMAT Problem Solving Question

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Figure 1
Correct Answer: B
  1. In working the problem, it is extremely important to remember that, by the rules of exponents, xY = 1/(x-Y)
    Figure 2
  2. Alternatively, you could do the problem like this:
  3. Plug in 1 for n to yield (.1*1)798/(.1*1)800, which is (.1)798/(.1)800 since any number multiplied by 1 is simply that number. In other words, .1*1 = .1
  4. Cancel 798 0.1's from the numerator and denominator. It helps to think of the expression as x798/x800, where x=0.1. This yields 1/x2, or 1/(.1)2.
  5. 0.1 = 1/10, so (.1)2=12/102, or 1/100.
  6. The number we are interested in is the reciprocal of (.1)2, that is 1/(.1)2, so the reciprocal of 1/100 is 100. The answer is B.

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