Sudheesh Singanamalla
Last Activity: 14 Years ago
nPr is the number of Permutations of 'n' items taken 'r' at a time.
nCr is the number of Combinations of 'n' items taken 'r' at a time.
nPr = n! / (n-r)!
nCr = n! / [ (n-r)! * r! ]
n factorial is the product of n terms and the number of terms preceding it
suppose 'n' is 5 then 5! = 5*4*3*2*1 = 120
similarly n! = n*(n-1)*(n-2)*(n-3)*.......................*3*2*1
nCr is the number of combinations possible .
eg. there are 52 cards in a well shuffled deck. how many combinations are there in which a player can draw only 2 cards at a time ?
nPr is the number of permutations (possbilities).
HERE ARE SOME QUESTIONS YOU CAN PRACTICE.
1. There are four bus routes between A and B; and three bus routes
between B and C. A man can travel round-trip in number of ways by bus from A to C
via B. If he does not want to use a bus route more than once, in how many ways can
he make round trip?
2. How many numbers are there between 99 and 1000 having 7 in the units place?
Good Luck in your IIT-JEE preparation.
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