Question

in how many ways can 4 identical white balls and 6 identical black balls be arranged in a row so that no white balls occur together

Answer 1

Please refer to the above image. Since no white balls can be next to each other, the much be in between the black balls.

According to this theory, there are 7 places which the white balls may occupy. We need to choose 4 out of these 7 spaces. Hence, we will apply:

7C4
= 35