How many different bit strings are there of length 6 that contain the string 0000?

It can be 100001, 100000,000001,000000

Hence, answer is 4.

its also can be found through 2C2 * 2 = 2!/0! * 2 = 2*2 = 4

Explanation:

The answer is straight forward, we have 2 empty places and we can select from 2 items, and hence its 2C2, and now we can arrange them as well, and since we can arrange in 2 ways, hence a total number of possibility = 2 * 2C2 = 4, which is the required answer.