GMAT Quant Questions | Probability Q5

Complementary Events | Exhaustive Events

This GMAT practice question is a medium difficulty Probability question and is a problem solving question. The question is a classic example of how it makes sense to first find the probability of the event complementary to the event asked and then compute the required probability.

Question 5: A man can hit a target once in 4 shots. If he fires 4 shots in succession, what is the probability that he will hit his target?

  1. 1
  2. \\frac{1}{256}\\)
  3. \\frac{81}{256}\\)
  4. \\frac{175}{256}\\)
  5. \\frac{144}{256}\\)

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Explanatory Answer | GMAT Probabiility Practice Q5

Step 1 of solving this GMAT Probabiility Question: Find the probability of the complementary event

The man will hit the target if he hits it once or twice or thrice or all four times in the four shots that he takes.
So, the only possibility when the man will not hit the target is when he fails to hit the target in even one of the four shots that he takes.
The event of not hitting the target even once is the complement of the event of hitting the target at least once.

The probability that he will not hit the target in a shot = 1 - \\frac{1}{4}\\) = \\frac{3}{4}\\)
Therefore, the probability that he will not hit the target in any of the four shots = \\frac{3}{4}\\) × \\frac{3}{4}\\) × \\frac{3}{4}\\) × \\frac{3}{4}\\) = \\frac{81}{256}\\)

Step 2 of solving this GMAT Probabiility Question: Find the probability of the required event

The probability that he will hit the target at least in one of the four shots = 1 - {probability of not hitting the target even once}
= 1 - \\frac{81}{256}\\) = \\frac{175}{256}\\)

Choice D is the correct answer.



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