Permutations & Combinations
Important Instructions
On a railway line there are 20 stops. A ticket is needed to travel between any 2 stops. How many different tickets would the government need to prepare to cater to all possibilities?
Answer: C
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How many four digit numbers can be formed using the digits {1, 3, 4, 5, 7,9}(repetition of digits is not allowed)?
Answer: A
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There are 18 stations between Hyderabad and Bangalore. How many second class tickets have to be printed, so that a passenger can travel from any station to any other station?
Answer: D
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There are 30 people in a group. If all shake hands with one another , how many handshakes are possible?
Answer: B
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A box contains 2 white balls, 3 black balls and 4 red balls. In how many ways can 3 balls be drawn from the box, if at least one black ball is to be included in the draw?
Answer: C
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How many 3-digit numbers can be formed from the digits 2, 3, 5, 6, 7 and 9, which are divisible by 5 and none of the digits is repeated?
Answer: D
Since each desired number is divisible by 5, so we must have 5 at the unit place. So, there is 1 way of doing it.
The tens place can now be filled by any of the remaining 5 digits (2, 3, 6, 7, 9). So, there are 5 ways of filling the tens place.
The hundreds place can now be filled by any of the remaining 4 digits. So, there are 4 ways of filling it.
Required number of numbers = (1 x 5 x 4) = 20.
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In how many different ways can the letters of the word 'CORPORATION' be arranged so that the vowels always come together?
Answer: D
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There are 8 routes from London to Delhi. And there are 6 routes from Delhi to Tokyo. In how many different ways can Raj travel from London to Tokyo via Delhi?
Answer: B
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A question paper had 10 questions. Each question could only be answered as true(T) of False(F). Each candidate answered all the questions, Yet no two candidates wrote the answers in an identical sequence. How many different sequences of answers are possible?
Answer: D
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In a class, there are 15 students. During a Christmas party all of them shook hands with each other only once. How many handshakes took place in the class?
Answer: C
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Topics
- Number System
- H.C.F. & L.C.M.
- Decimal Fractions
- Simplification
- Average
- Problems on Numbers
- Problems on Ages
- Percentage
- Profit & Loss
- Ratio & Proportion
- Time & Work
- Pipes & Cistern
- Time & Distance
- Problems on Trains
- Boats & Streams
- Simple Interest
- Compound Interest
- Area
- Volume & Surface Areas
- Mensuration
- Races & Games of Skill
- Clocks
- Permutations & Combinations
- Probability
- Odd Man Out & Series
- Algebra