The lifetimes of 100 electric bulbs were tested in a laboratory. The results were recorded in the following ‘more than’ cumulative frequency table.
Lifetime more than 200 h : 100
Lifetime more than 300 h : 97
Lifetime more than 400 h : 90
Lifetime more than 500 h : 72
Lifetime more than 600 h : 40
Lifetime more than 700 h : 16
Lifetime more than 800 h : 5
Using class intervals of width 100 h (200–300, 300–400, … , 800–900), answer the following.
(i) Convert the information into a simple frequency distribution table.
(ii) Draw a histogram for the obtained frequency distribution on graph paper.
(iii) Using cumulative frequencies, identify the class interval that contains the longest-lasting 10 % of bulbs.
(iv) Estimate how many bulbs failed before completing 550 hours of use.