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How many ways are there to select exactly four clocks from a store with 10 wall-clocks and 16 stand-clocks?(a) 325(b) 468(c) 398(d) 762I had been asked this question by my school teacher while I was bunking the class.The question is from Multiplication Theorem on Probability in portion Discrete Probability of Discrete Mathematics

Answer»

Correct option is (a) 325

To ELABORATE: To choose any clock for the FIRST pick, there are 10+16=26 options. For the second choice, we have 25 clocks left to choose from and so on. Thus, by the rule of product, there are 26 * 25 * 24 * 23 = 650 POSSIBLE ways to choose exactly four clocks. However, we have counted every clock combination TWICE. Hence, the correct number of possible ways are 650/2 = 325.



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