The following table gives the life times of 400 neon lamps:
| Life time (in hours) | Number of lamps |
|---|---|
| 300 - 400 | 14 |
| 400 - 500 | 56 |
| 500 - 600 | 60 |
| 600 - 700 | 86 |
| 700 - 800 | 74 |
| 800 - 900 | 62 |
| 900 - 1000 | 48 |
(i) Represent the given information with the help of a histogram.
(ii) How many lamps have a life time of more than 700 hours?
(i) Steps of construction of histogram :
Plot the lifetime (in hours) on x-axis.
Plot the number of lamps on y-axis by taking 1 unit = 10 lamps.
Since, the scale on x-axis starts at 300, a break (kink) is shown near the origin on x-axis to indicate that the graph is drawn to scale beginning at 300.
To represent our first Head, i.e., (300-400) we draw a rectangular bar with width 1 unit and height 14 units.
Similarly, other Heads are represented without leaving a gap between two consecutive bars.
(ii) The number of neon lamps having their lifetime of more than 700 hours lies in the class intervals 700 – 800, 800 – 900 and 900 – 1000.
The corresponding frequencies when added up will be (74 + 62 + 48) = 184 lamps.
Hence, 184 lamps have a life time of more than 700 hours.