The average of five consecutive numbers is 53. What is the biggest of these numbers?

55

Five consecutive numbers can be written as: n, n+1, n+2, n+3, n+4

                  where, n is natural number

Average = $\frac{Sum\; of\; these\; numbers}{5}$

             = $\frac{n+n+1+n+2+n+3+n+4}{5}$

             = $\frac{5n+10}{5}$

             = n+2

We know, the average = 53

⇒ n+2 = 53

⇒   n   = 51

The biggest number among these numbers is n+4 = 51 + 4 = 55