Question
A box consists of 125 apples out of which 25 are rotten.
Khushboo comes to buy non-rotten apple. The shopkeeper takes out two apples and hands it over to Khushboo one after another. If the apple is not rotten she buys else the shopkeeper keeps them back. What is the probability that Khushboo buys at least one apple?Solution
Case I: Khushboo buys two apples
Probability of buying first apple = (125 - 25)/125 = 100/125 = 4/5
Probability of buying second apple = (100 - 1)/(125 - 1) = 99/124
∴ Probability of buying two apples = (4/5) X (99/124) = 99/155
Case II: Khushboo buys one apple
Probability that she is offered non-rotten apple in first attempt and rotten in second = 100/125 X 25/124 = 5/31
Probability that she is offered rotten apple in first attempt and non - rotten in second = 25/125 X 100/125 = 4/25
∴ Required Probability = 99/155 + 5/31 + 4/25 = 24/25
- A dog sees a rabbit 75 meters away and begins chasing it. The rabbit runs at 14 m/sec, while the dog runs at 20 m/sec. How much time will it take for the d...
A man walks at 5 km/h for 2 hours and then at 4 km/h for 1.5 hours. Find the total distance covered and his average speed for the whole journey.
A Bus moving at a speed of 's' km/h can pass a stationary person in 16 seconds and a tunnel Bridge that is 240 meters long in 28 seconds. Determine the ...
Two cyclists are riding towards one another at speeds of 36 km/h and 27 km/h. What will be the distance between them 5 seconds before they meet?
- Amit covers a journey in 12 hours at a constant speed of 18 km/h. At what speed should he travel to cover the same distance in just 9 hours?
A policeman saw a thief from a distance of 450 m. When the policeman started chasing him, the thief also started running. The ratio of speeds of the th...
A reporter gets Rs. 40 per km for taxi travel and Rs. 20 per km for auto travel. In one week, he travelled 120 km and claimed Rs. 3600. How many km did ...
A thief is spotted by a policeman from a distance of 200 meters. When the policeman starts the chase, the thief also starts running. If the speed of the...
A motor-cycle covers 90 km with a speed of 40 km/hr. find the speed of the motor-cycle for the next 90 km journey so that the average speed of the whole...
- Vikram drives for 15 hours at a speed of 22 km/h. If he wants to travel the same distance in 11 hours, what speed should he maintain?
Relevant for Exams:
