Question

A box contains 100 round discs, 50 square - shaped discs and 30 triangular discs. All the discs are made up of iron and have an equal probability of getting attracted by a magnet. If a magnet which can attract only one disc in one pass and the disc is passed over them twice. What is the probability that both times a triangular disc is attracted? The disc attracted in one pass does not fall into box again, however each time a square shaped disc is kept into the box.

• A. (A) 29180
• B. (B) 291074
• C. (C) 136
• D. (D) 291080

Answer 1

Answer: (D)

(D) 291080

Answer 2

Explanation:
Given:A box contains 100 round discs, 50 square-shaped discs and 30 triangular discs.Probability = Number of observation Total number of observation Total number of discs =180Total number of triangular discs =30The probability that in first pass a triangular disc is attracted =30180 =16The first disc is kept aside and one square disc is kept inside.The probability that in second pass a triangular disc is attracted =29180 Required Probability =16×29180=291080∴ Required Probability is 291080Hence, the correct option is (D).