SOLUTION: Please,solve the following two questions. I need your kind and expert help. God bless you. Problem 1: A box contains 5 red marbles and three white marbles. A marble

Question 421275: Please,solve the following two questions. I need your kind and expert help.
God bless you.
Problem 1:
A box contains 5 red marbles and three white marbles. A marble will be drawn at random from the box. If the marble is red, the drawing stops. If the marble is white,it is laid aside and another marble is drawn.This process continues untill a red marble is drawn. Draw a probability tree for this experiment and find the probability that the drawing stops on the second draw. The second or third draw?
Problem 2:
A True-False exame has 10 questions.Linda fills out the answer sheet simply by guessing, without even reading the questions. What is the probability that she will make 90% on the exam? What is the probability that she will make 80%? What is the probability that she will make 100% ? What is the probability that she will make at least 80% ?
Answer by sudhanshu_kmr(1152) (Show Source): You can put this solution on YOUR website!

5 red , 3 white marbles.

The probability that the drawing stops on the second draw = 3/8 * 5/7 = 15/56

probability that the drawing stops on second or third draw =
probability that stop on second + probability that stop on third draw
= 15/56 + 3/8 * 2/7 * 5/6
= 15/56 + 5/56
= 20/56
= 5/14

2. It is binomial probability .....
probability that make 90%, it means 9 right, 1 wrong = 10C9 *(1/2)^9 * (1/2)^1

probability that make 80% = 10C8* (1/2)^8 * (1/2)^2

probability that make 100% = 10C10* (1/2)^10 * (1/2)^0

similarly for at least 80% =
(probability of make 80%) + (probability of 90%) + (probability of 100%)

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