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- Question
In a class, there are 15 boys and 10 girls. Three students are selected at random. The probability that 1 girl and 2 boys are selected, is:
Options- A.
21 46 - B.
25 117 - C.
1 50 - D.
3 25 - Correct Answer
-
21 46
ExplanationLet S be the sample space and E be the event of selecting 1 girl and 2 boys.Then, n(S) = Number ways of selecting 3 students out of 25 = 25C3 ` = (25 x 24 x 23) (3 x 2 x 1) = 2300. n(E) = (10C1 x 15C2) = [ 10 x (15 x 14) ] (2 x 1) = 1050. ∴ P(E) = n(E) = 1050 = 21 . n(S) 2300 46
More questions
- 1. A and B together can complete a work in 3 days. They started together but after 2 days, B left the work. If the work is completed after 2 more days, B alone could do the work in how many days?
Options- A. 5
- B. 6
- C. 7
- D. 10 Discuss
Correct Answer: 6
Explanation:
(A + B)'s 2 day's work = 2 x (1/3) = 2/3
Remaining work = 1 - (2/3) = 1/3
A will complete 1/3 work in 2
A will complete 1 work in 6
A's 1 days work = 1/6
B's 1 day's work = (1/3) - (1/6) = 1/6
? B will take 6 days to complete the work alone.- 2. A wheel makes 1000 revolutions in covering a distance of 88 km. the diameter of the wheel is?
Options- A. 24 meters
- B. 40 meters
- C. 28 meters
- D. 14 meters Discuss
Correct Answer: 28 meters
Explanation:
Distance covered in one revolution = total distance travelled / total number of revolution.
= ( 88 x 1000) / 1000 m
= 88 m
We know that the distance covered in one revolution = circumference of the wheel.
? ?d = 88
? 22d / 7 = 88
? d = 28 m- 3. 25, 36, 49, 81, 121, 169, 225
Options- A. 36
- B. 49
- C. 121
- D. 169 Discuss
Correct Answer: 36
Explanation:
The numbers are squares of odd natural numbers, starting from 5 up to 15.So, 36 is wrong.
- 4. (.896 x .752 +.896 x .248) / (.7 x .034 + .7 x.966) =?
Options- A. 1.28
- B. 0.976
- C. 12.8
- D. 9.76 Discuss
Correct Answer: 1.28
Explanation:
Given expression = (.896 x .752 +.896 x .248) / (.7 x .034 + .7 x.966)
=.[896 x (.752+.248)] / [.7 x (.034+.966)]
= .(896 x 1) / ( .700 x 1)
=896/700
= 1.28- 5. Einstein goes from Ahmedabad To Lucknow at the speed of 40 km/hr and returned at the speed of 60 km/hr .the average speed of Einstein during the whole journey is
Options- A. 48 km/hr
- B. 24 km/hr
- C. 50 km/hr
- D. none of these Discuss
Correct Answer: 48 km/hr
Explanation:
Average speed =2 x 40 x 60 / ( 40+ 60)
= 4800 / 100
= 48 km/hr- 6. Today is Monday. After 61 days, it will be
Options- A. Wednesday
- B. Saturday
- C. Tuesday
- D. Thursday Discuss
Correct Answer: Saturday
Explanation:
Each day of the week is repeated after 7 days.
So, after 63 days, it will be Monday.
After 61 days, it will be Saturday.- 7. 9548 + 7314 = 8362 + (?)
Options- A. 8230
- B. 8410
- C. 8500
- D. 8600
- E. None of these Discuss
Correct Answer: 8500
Explanation:
9548 16862 = 8362 + x + 7314 x = 16862 - 8362 ----- = 8500 16862 -----
- 8. The true discount on a certain sum due 1 yr hence at 30% per annum, is ? 240. What is the banker' discount on the same sum for the same time and at the same rate?
Options- A. ? 400
- B. ? 212
- C. ? 312
- D. ? 445 Discuss
Correct Answer: ? 312
Explanation:
We know that
BG = SI on TD = (240 x 30 x 1 x 1)/100
= ? 72
BG = BD - TD
? BD = BG + TD
= 72 + 240
= ? 312- 9. Calendar of month July is same as that of which month of previous year.
Options- A. May
- B. September
- C. April
- D. None of these Discuss
Correct Answer: May
Explanation:
If previous year is leap year then calendar of May is similar to July
- 10. A coin is successively tossed two times. Find the probability of getting? (1) exactly one head (2)at least one head
Options- A. 1/2 , 3/4
- B. 2/3, 1/4
- C. 1/4, 4/5
- D. 1/2, 2/3 Discuss
Correct Answer: 1/2 , 3/4
Explanation:
In tossing a coin 2 times the sample space is 4 i,e (H, H), (H, T), (T, H), (T, T)
(1) If A1 denotes exactly one head
then A1 = {(H, T) (T, H) }
So, P(A1 ) = 2/4 = 1/2
(2) If A denotes at least one head
then A = {(H, T) (T, H) (H, H)}
? A = {(H, T) (T, H) (H, H )}
? P(A) = 3/4
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