Question

In how many ways 21 red balls and 19 blue balls can be arranged in a row so that no two blue balls are together
Hint: Ans:1540​

Answer 1

In how many ways 21 red balls and 19 blue balls can be arranged in a row so that no two blue balls are together?

As there are 21 red balls and 19 blue balls.

So there can be 22 different positions for blue balls ( because we can't arrange two blue balls together).

Applying concept,

Total ways = 22C19

= 22!/19!(22-19)!

= 22!/19!*3!

= 22*21*20*19!/19!*3!

= 22*7*10

= 1540.

Answer 2

dear Fatima sister.......

the x's mark permissible positions for the blue balls in the pattern

x 1 x 2 x ........ x 20 x 21 x , ie 22 places for 19 blue balls

22c19 = 1540 <-

hope I answered your question....