How many ternary strings of length 10 that contain exactly 2 1s and 3 2s....
How many ternary strings of length 10 that contain exactly 2 1s and 3 2s. Since it must contain exactly 2 1s and 3 2s the other 5 spaces must be 0s.But how many ways can we arrange this?
Answer & Explanation
(using classical formula .)
You first choose the 2 places (among 10) where you place the 1s, then, for each of these choices, you can select the 3 places where you will place a 2 (in each case among the remaining 8 places). No more choices for the other places where the zeros will be placed.