Probability Model Questions Set 1 Section-Wise Topic Notes With Detailed Explanation And Example Questions
MOST IMPORTANT quantitative aptitude - 1 EXERCISES
The following question based on Probability topic of quantitative aptitude
Study the given information carefully and answer the questions that follow.
A basket contains 4 red, 5 blue and 3 green marbles.
If two marbles are drawn at random, what is the probability that both are red ?
(a) $1/2$
(b) $1/6$
(c) $3/7$
(d) $2/11$
e) None of these
The correct answers to the above question in:
Answer: (e)
Total possible result n(S) = $^{12}C_{2}$ = ${12 × 11}/{1 × 2}$ = 66
Total number of event = n(E) $^4 C _2$ = ${4 × 3}/{1 × 2}$ = 6
∴ Required probability = ${n(E)}/{n(S)}$ = $6/{66}$ = $1/{11}$
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Question : 1
A dice is thrown. What is the probability that the number shown on the dice is not divisible by 3?
a) $2/3$
b) $2/5$
c) $1/3$
d) $1/4$
e) None of these
Answer »Answer: (a)
S = {1, 2, 3, 4, 5, 6}; n(S) = 6
E(not divisible by 3) = 1, 2, 4, 5}, n(E) = 4
∴ P(not divisible by 3) = $4/6$ = $2/3$
Question : 2
Directions :
Study the given information carefully and answer the questions that follow.
A basket contains 4 red, 5 blue and 3 green marbles.
If three marbles are picked at random, what is the probability that at least one is blue ?
a) $37/44$
b) $7/44$
c) $7/12$
d) $5/12$
e) None of these
Answer »Answer: (a)
Total possible result = n(S) = $^{12} C_3$.
= ${12 × 11 × 10}/{1 × 2 × 3}$ = 220 Total number of event = n(E)
Except blue marbles, selection of 3 marbles out of 7 marbles
= $^{7}C_3$ = ${7 × 6 × 5}/{1 × 2 × 3}$ = 35
∴ Required probability = $(1 -{35}/{220}) = (1 - {7}/{44})$ = ${37}/{44}$
Question : 3
3 digits are chosen at random from 1,2,3,4,5,6,7,8 and 9 without repeating any digit. What is the probability that their product is odd?
a) $5/108$
b) $8/42$
c) $2/3$
d) $5/42$
e) $9/42$
Answer »Answer: (d)
Let E be the event of selecting the three numbers such that their product is odd and S be the sample space.
For the product to be odd, 3 numbers chosen must be odd.
∴ n(E) = $^5C_3$
n(S) = $^9C_3$
∴ P (E) = ${n(E)}/{n(S)}$ = ${^5C_3}/{^9C_3}$ = ${5}/{42}$
Question : 4
In a box carrying one dozen of oranges, one-third have become bad. If 3 oranges are taken out from the box at random, what is the probability that at least one orange out of the three oranges picked up is good?
a) $54/55$
b) $3/55$
c) $1/55$
d) $45/55$
e) None of these
Answer »Answer: (a)
P(At least one good) = 1 – P(All bad)
= 1 - ${{^4C_3}/{^12C_3}}$ = 1 - ${4/{220}}$ = 1 -${1/{55}}$= ${54}/{55}$
Question : 5
A basket contains three blue and four red balls. If three balls are drawn at random from the basket, what is the probability that all the three are either blue or red ?
a) $1/7$
b) $3/28$
c) 1
d) $3/14$
e) None of these
Answer »Answer: (e)
Probability to be a Blue = ${^3C_3}/{^7C_3}$
Probability to be a Red = ${^4 C_3}/{^7C_3}$
Required probability = ${^3 C_3}/{^7 C_3}$ + ${^4 C_3}/{^7C_3}$ = $2/{35}$
Question : 6
Two packs of cards are thoroughly mixed and shuffled and two cards are drawn at random, one after the other. What is the probability that both of them are jacks?
a) $2/13$
b) $1/169$
c) $1/13$
d) $7/1339$
e) $1/179$
Answer »Answer: (d)
Total number of cards = 104 = 2 × 52
and total number of jacks = 8 = 2 × 4
∴ Probability for the jack in first draw = $8/{104}$
and probability for the jack in second draw = $7/{103}$
Since both the events are independent events.
Hence the probability that both of them are jacks.
= ${8}/{104}$ × ${7}/{103}$ = $7/{1339}$
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