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Question
The following table gives the duration of movies in minutes:
| Duration | 100 – 110 | 110 – 120 | 120 – 130 | 130 – 140 | 140 – 150 | 150 – 160 |
| No. of movies | 5 | 10 | 17 | 8 | 6 | 4 |
Using step-deviation method, find the mean duration of the movies.
Solution
| Duration (in minutes) |
No. of movies `bb(f_i)` |
`bb(x_i)` | `bb(u_i = (x_i - A)/h)` | `bb(f_iu_i)` |
| 100 – 110 | 5 | 105 | –3 | –15 |
| 110 – 120 | 10 | 115 | –2 | –20 |
| 120 – 130 | 17 | 125 | –1 | –17 |
| 130 – 140 | 8 | 135 = A | 0 | 0 |
| 140 – 150 | 6 | 145 | 1 | 6 |
| 150 – 160 | 4 | 155 | 2 | 5 |
| Total | 50 | –38 |
`barx = (sumf_iu_i)/(sumf) xx h`
= `135 + ((-38))/50 xx 10`
= 135 – 7.6
= 127.4
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