Combinations
Combination
Each of the groups or selections that can be made by taking some or all of a number of things without considering the arrangement or order is called a combination.
Thus, the selections that can be made by taking the letters a, b and c two at a time are three. i.e., ab, bc and ac. These three groups or selections are called the combination of three things taken two at a time.
The number of combinations of n dissimilar things taken r at a time is calculated using the expression
For Example: The number of selection of 6 dissimilar things taken 4 at a time is
The number of combinations of n dissimilar things taken all at a time is
Also,
For Example: The number of selection of 3 dissimilar things taken all at is a time
Illustration: Each person's performance compared with all other persons is to be done to rank them subjectively. How many comparisons are needed in total, if there are 11 persons ?
(a) 66 (b) 55 (c) 54 (d) 45
Answer : b
Solution Comparison is always done between two peoples, we have to select 2 persons among the 11 persons for a comparison. Hence
How many committee of five persons with a chairperson can be selected form 12 persons? | |||
| Right Option : B | |||
| View Explanation | |||
Students / Parents Reviews [10]
My experience with Abhyas academy is very good. I did not think that my every subject coming here will be so strong. The main thing is that the online tests had made me learn here more things.
Hiya Gupta
8thIt was good as the experience because as we had come here we had been improved in a such envirnment created here.Extra is taught which is beneficial for future.
Eshan Arora
8thAbhyas is a complete education Institute. Here extreme care is taken by teacher with the help of regular exam. Extra classes also conducted by the institute, if the student is weak.
Om Umang
10thI have spent a wonderful time in Abhyas academy. It has made my reasoning more apt, English more stronger and Maths an interesting subject for me. It has given me a habbit of self studying
Yatharthi Sharma
10thAbout Abhyas metholodology the teachers are very nice and hardworking toward students.The Centre Head Mrs Anu Sethi is also a brilliant teacher.Abhyas has taught me how to overcome problems and has always taken my doubts and suppoeted me.
Shreya Shrivastava
8thA marvelous experience with Abhyas. I am glad to share that my ward has achieved more than enough at the Ambala ABHYAS centre. Years have passed on and more and more he has gained. May the centre flourish and develop day by day by the grace of God.
Archit Segal
7thIt has a great methodology. Students here can get analysis to their test quickly.We can learn easily through PPTs and the testing methods are good. We know that where we have to practice
Barkha Arora
10thOne of the best institutes to develope a child interest in studies.Provides SST and English knowledge also unlike other institutes. Teachers are co operative and friendly online tests andPPT develope practical knowledge also.
Aman Kumar Shrivastava
10thBeing a parent, I saw my daughter improvement in her studies by seeing a good result in all day to day compititive exam TMO, NSO, IEO etc and as well as studies. I have got a fruitful result from my daughter.
Prisha Gupta
8thIt was a good experience with Abhyas Academy. I even faced problems in starting but slowly and steadily overcomed. Especially reasoning classes helped me a lot.
