The average of eighteen numbers is 42. The average of the last ten numbers is 40 and that of the first five numbers is 44. The seventh number is 6 less than the sixth and 7 less than the eighth number. The average of the sixth and the eighth number is:
Answer & explanation
Correct answer: option 2
Sum of 18 numbers is = 18 × 42 = 756
Sum of first 5 numbers is = 5 × 44 = 220
Sum of last 10 numbers = 10 × 40 = 400
Sum of 6th , 7th & 8th number = 756 - (220 + 400) = 136
Let seventh number = a , Then 6th number = a + 6 & 8th number = a + 7
ATQ ,
a + a + 6 + a + 7 = 136
3a = 123
a = 41
6th number = 41 + 6 = 47 & 8th number = 41 + 7 = 48
Average of 6th and 8th number = \(\frac{47 + 48 }{2}\) = 47.5