The average of 52, 71, 43, 22, a, and b is 55 and the average of 42, 45, 49, 51, 42, c, and d is 53. What is the average of a, b, c, and d?

71

Given,

          \(\frac{52 + 71 + 43 + 22 + a + b }{6}\) = 55

          ⇒ a + b = 142

          \(\frac{42 + 45 + 49 + 51 + 42 + c + d}{7}\) = 53

          ⇒ c + d = 142

Average of a, b, c and d = \(\frac{a + b + c + d}{4}\)

                                      = \(\frac{142 + 142}{4}\)

                                      = 71