Suppose you pick a marble from the bag that contains six blue marbles and nine r

Question

Suppose you pick a marble from the bag that contains six blue marbles and nine red marbles. You record the color, put the first marble back, and then you draw a second marble. What is the probability that both marbles drawn are red? A. 1/7 B. 12/35 C. 11/29 D. 17/29 E. 27/70 For questions 10 and 11, consider the following: suppose a certain drug test was evaluated to see how accurate it is. The following table gives the results for the test: What percentage of individuals given the drug test were given incorrect results? to the nearest tenth of a percent. A. 4.8% B. 6.5% C.7.1% D. 11.9% E. 27.3% What is the percent chance that a person selected at random would be a true posit given that they are drug users? In other words, what is the sensitivity of this test? Round to the nearest tenth of a percent. A. 90.6% B. 83.3% C. 80.0% D. 72.7% E. 27.3%

Explanation / Answer

Problem No.9

Bag contains 6 blue marbles and 9 red marbles, totalling to 15 marbles

In both first and second draw the selected marbles is to be of red color, so the probability of having both the marbles red, we get

9C2 / 15C2 .....................................................................................................................(1)

9C2 = 9!/7!*2! = 9*8*7!/7!*2 = 72/2 =36 .......................................................................(a)

15C2 = 15!/13!*2! = 15*14*13!/13!*2 = 15*7 = 105 ......................................................(b)

Putting value a & b in 1 we get

9C2 / 15C2 = 36/105 = 12/35

Problem No. 10

Drug user:

Test positive (correct) - 80

Test negative (incorrect) - 30

Not a drug user:

Test Positive (incorrect) - 20

Test Negative (correct) - 290

Therefore the no.of correct and incorrect results are 370 and 50 respectively out of total 420 results.

The percentage of individuals given the drug test were given the incorrect results is (No.of incorrect results)*100 /(total results)

=50*100/420 = 11.9%

Problem No.11

Drug users positive for test = 80

Drug users negative for test= 30

Total drug users = 110

Percent chance that a person selected at random would be true positive

=(drug users with positive results)*100/(total no.of drug users)

= 80*100/110 = 72.7%

Related Questions

Navigate

• Browse (All)
• Browse S
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.