Aptitude Day 156

Problems on Average:

 1. The average of the two-digit numbers, which remain the same when the digits interchange their positions, is:

Solution:

                    Average = Sum of observations/ Number of observations

                                    = (11+22+33+44+55+66+77+88+99)/ 9

                                    = [(11+99)+(22+88)+(33+77)+(44+66)+55]/9

                                    = [4(110)+55]/9

                                    = 495/9

                                    = 55.

2. The average of non-zero number and its square is 9 times the number. The number is:

Solution:

                 (x+x²)/2 = 9x

                  x+x² = 18x

                  x² -17x = 0

                  x(x-17) = 0

                  x = 0, 17.

                The non-zero value is 17.