Given that \(n = 10\) and \(\sum d^{2} = 20\), calculate the Spearman's rank correlation coefficient.

Find the variance of 11, 12, 13, 14 and 15.

A fair coin is tossed 3 times. Find the probability of obtaining exactly 2 heads.

A box contains 14 white balls and 6 black balls. Find the probability of first drawing a black ball and then a white ball without replacement.

Given that \(r = 3i + 4j\) and \(t = -5i + 12j\), find the acute angle between them.