MEDIUM
JEE Main/Advance
IMPORTANT
Earn 100

Let Pn denotes the number of ways of selecting 3 people out of 'n' sitting in a row if no two of them are consecutive and Qn is the corresponding figure when they are in a circle. If Pn-Qn=6, then 'n' is equal to

Important Questions on Permutation and Combination

MEDIUM
JEE Main/Advance
IMPORTANT
The number of ways selecting 8 books from a library which has 10 books each of Mathematics, Physics, Chemistry and English, if books of the same subject are alike, is N2-4 then N is equal to
MEDIUM
JEE Main/Advance
IMPORTANT
The number of three digit numbers of the form xyz such that x<y and zy is N then N-225 is equal to
MEDIUM
JEE Main/Advance
IMPORTANT
In an examination, a candidate is required to pass in all the four subjects he is studying. The number of ways in which he can fail is
EASY
JEE Main/Advance
IMPORTANT
The kindergarten teacher has 25 kids in her class. She takes 5 of them at a time, to zoological garden as often as she can, without taking the same 5 kids more than once. Then the number of visits, the teacher makes to the garden exceeds that of a kid by:
MEDIUM
JEE Main/Advance
IMPORTANT
A student has to answer 10 out of 13 questions in an examination. The number of ways in which he can answer if he must answer atleast 3 of the first five questions is:
MEDIUM
JEE Main/Advance
IMPORTANT
Number of ways in which 3 different numbers in A.P. can be selected from 1, 2, 3, .n is
EASY
JEE Main/Advance
IMPORTANT
2m white identical coins and 2n red identical coins are arranged in a straight line with m+n identical coins on each side of a central mark. The number of ways of arranging the identical coins, so that the arrangements are symmetrical with respect to the central mark.
EASY
JEE Main/Advance
IMPORTANT
The number of ways in which 10 students can be divided into three teams, one containing 4 and others 3 each, is