Find the number of different ways of placing 15 balls in a row given that 4 are red, 3 are yellow, 6 are black and 2 are blue.
My own calculation is 6912 but I don't have the real answer.
My own calculation is 6912 but I don't have the real answer.
-
the permutation formula when r1,r2,r3,... objects from n are identical is
n!/(r1*r2!*r3!....) , so
# of ways = 15!/(4!*3!*6!*2!) = 6,306,300 <--------
n!/(r1*r2!*r3!....) , so
# of ways = 15!/(4!*3!*6!*2!) = 6,306,300 <--------
-
just as you have to multiply to account for different objects,
you need to divide to "take out" arrangements that are the same
you need to divide to "take out" arrangements that are the same
Report Abuse
-
15!/(4!3!6!2!)=900900 by my reckoning