Six numbers are arranged in decreasing order. The average of the first five numbers is 30 and the average of the last five numbers is 25. The difference of the first and the last numbers is

Numbers are
x > y > z > p > q > r
According to the question,
Average of first five numbers = 30
Sum of first five numbers
= a + y + z + p + q = 5 × 30 = 150.....(i)
Average of last five numbers
= y + z + p + q + r = 5 × 25 = 125.....(ii)
By equation (i) and (ii)
a - r = 150 - 125 = 25