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Two marbles are selectod randomly five a box containing 5 red, 7 white and 8 thore marbles one after the other withoet replacement. Find the probutility that (a) both are red; (b) one is white and the other is blase, (c) both are of the mane coloer

Ask by Jimenez Rowe. in Nigeria
Feb 19,2025

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Answer

(a) Probability both marbles are red: 1/19 (b) Probability one marble is white and the other is blue: 28/95 (c) Probability both marbles are the same color: 59/190

Solution

We have a box with 5 red, 7 white, and 8 blue marbles (5 + 7 + 8 = 20 total). Two marbles are drawn one after the other without replacement. (a) Probability both are red:  • The probability the first marble is red is 5/20.  • Once a red is removed, 4 red remain out of 19 total.  • So, P(both red) = (5/20) × (4/19) = 20/380 = 1/19. (b) Probability one is white and the other is blue: This can happen in two orders.  Order 1: White then blue:   • First marble white: 7/20.   • Then blue: 8/19.   • So, probability = (7/20) × (8/19).  Order 2: Blue then white:   • First marble blue: 8/20.   • Then white: 7/19.   • So, probability = (8/20) × (7/19).  Adding these:   P(white and blue in any order) = (7×8/20×19) + (8×7/20×19) = (56 + 56) / (380) = 112/380.   Simplify by dividing numerator and denominator by 4: 112/380 = 28/95. (c) Probability both marbles are of the same color: We sum the probabilities for red–red, white–white, and blue–blue.  • Red–red: As in (a): (5/20) × (4/19) = 10/190.  • White–white:   – First white: 7/20.   – Then white: 6/19.   – So, = (7/20) × (6/19) = 42/380 = 21/190.  • Blue–blue:   – First blue: 8/20.   – Then blue: 7/19.   – So, = (8/20) × (7/19) = 56/380 = 28/190.  Total probability = (10 + 21 + 28) / 190 = 59/190. Thus, the answers are:  (a) 1/19,  (b) 28/95, and  (c) 59/190.

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The Deep Dive

To calculate the probabilities, we'll first determine the total number of marbles in the box, which is 5 red + 7 white + 8 blue = 20 marbles. (a) The probability that both marbles selected are red is: P(both red) = (5/20) * (4/20) = 1/20. (b) The probability that one is white and the other is blue can be calculated in two ways (either the first is white and the second is blue or vice versa): P(white first, blue second) = (7/20) * (8/20) = 56/400. P(blue first, white second) = (8/20) * (7/20) = 56/400. Total = 56/400 + 56/400 = 112/400 = 7/25. (c) The probability that both are of the same color takes into account the cases for red, white, and blue: P(both red) = 1/20 (calculated earlier), P(both white) = (7/20) * (6/20) = 21/400, P(both blue) = (8/20) * (7/20) = 56/400. So, P(same color) = 1/20 + 21/400 + 56/400 = 20/400 + 21/400 + 56/400 = 97/400. Thus: (a) P(both red) = 1/20, (b) P(one white and one blue) = 7/25, (c) P(both same color) = 97/400.

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