If 6 boys and 3 girls are to be seated in a row for a photograph, then the probability that the end seats are occupied by the girls and no two girls are side by side is

A bag contains 23 balls, of which 7 are identical. The number of ways of selecting 12 balls from the bag is....

The approximate value of $(0.007)^{\frac{1}{3}}$ is

If $33\theta = \pi$, then the value of $\cos\theta \cos2\theta \cos4\theta \cos8\theta \cos16\theta$ is