Mathematics
The following table gives the life time in days of 100 electricity tubes of a certain make :
| Lifetime in days | No. of tubes |
|---|---|
| less than 50 | 8 |
| less than 100 | 23 |
| less than 150 | 55 |
| less than 200 | 81 |
| less than 250 | 93 |
| less than 300 | 100 |
Find the mean lifetime of electricity tubes.
Measures of Central Tendency
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Answer
We construct the following table :
| Lifetime in days (Classes) | Class mark (yi) | No. of tubes (Cumulative frequency) | Frequency (fi)) | fiyi |
|---|---|---|---|---|
| 0 - 50 | 25 | 8 | 8 | 200 |
| 50 - 100 | 75 | 23 | 23 - 8 = 15 | 1125 |
| 100 - 150 | 125 | 55 | 55 - 23 = 32 | 4000 |
| 150 - 200 | 175 | 81 | 81 - 55 = 26 | 4550 |
| 200 - 250 | 225 | 93 | 93 - 81 = 12 | 2700 |
| 250 - 300 | 275 | 100 | 100 - 93 = 7 | 1925 |
| Total | 100 | 14500 |
∴ Mean = = 145
Hence, mean of the following distribution is 145 days
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