The following table shows the distribution of life time of 350 radio tubes : Lifetime in hrs 300-400 400-500 500-600 600-700 No. of tubes 6 18 73 165 Lifetime in hrs 700-800 800-900 900-1000 No. of tubes 62 22 4Assuming that class frequencies are evenly distributed within the corresponding classes, find the percentage of tubes having life time between 650 hours and 850 hours

The correct answer is (c).

The total number of tubes is 350. The number of tubes with lifetime between 650 and 850 hours is 165 + 62 = 227. The percentage of tubes with lifetime between 650 and 850 hours is 227/350 = 64.86%, which is approximately 65%.

Option (a) is incorrect because it is the average lifetime of all the tubes. Option (b) is incorrect because it is the average lifetime of the tubes with lifetime between 650 and 850 hours. Option (d) is incorrect because it is the lifetime of the tube with the 64th highest lifetime.