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Probability and Statistics

GATE CSE 2016 Set 2 · Q5

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Suppose that a shop has an equal number of LED bulbs of two different types. The probability of an LED bulb lasting more than 100 hours given that it is of Type 1 is 0.7, and given that it is of Type 2 is 0.4. The probability that an LED bulb chosen uniformly at random lasts more than 100 hours is __________.

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Official answer: 0.55

Probability and Statistics

Let T1T_1 and T2T_2 denote the events that a randomly chosen bulb is of Type 1 and Type 2, respectively.

Since the shop has an equal number of bulbs of both types:

P(T1)=P(T2)=0.5P(T_1) = P(T_2) = 0.5

Let EE be the event that a bulb lasts more than 100 hours. The given conditional probabilities are:

P(E∣T1)=0.7P(E \mid T_1) = 0.7
P(E∣T2)=0.4P(E \mid T_2) = 0.4

By the Law of Total Probability:

P(E)=P(E∣T1)P(T1)+P(E∣T2)P(T2)P(E) = P(E \mid T_1)P(T_1) + P(E \mid T_2)P(T_2)
P(E)=(0.7)(0.5)+(0.4)(0.5)=0.35+0.20=0.55P(E) = (0.7)(0.5) + (0.4)(0.5) = 0.35 + 0.20 = 0.55

Thus, the required probability is 0.55.

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This Probability and Statistics previous year question is Q5 of the GATE CSE 2016 Set 2 paper. Find more GATE CSE PYQs on Probability and Statistics in Engineering Mathematics, or browse all GATE CSE PYQs.

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Probability and Statistics has 46 GATE CSE PYQs across 23 papers from 2011 to 2026. 11 of them are 1-mark NAT questions like this one, and it is the only one in GATE CSE 2016 Set 2.

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GateAI solution cardGATE CSE 2016 Set 2 · Q5 · NAT

Suppose that a shop has an equal number of LED bulbs of two different types. The probability of an LED bulb lasting more than 100 hours given that it is of Type 1 is 0.7, and given that it is of Type 2 is 0.4. The probability that an LED bulb chosen uniformly at random lasts more than 100 hours is …

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