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Question
Weekly income of 600 families is tabulated below:
| Weekly income (in Rs) |
Number of families |
| 0 – 1000 | 250 |
| 1000 – 2000 | 190 |
| 2000 – 3000 | 100 |
| 3000 – 4000 | 40 |
| 4000 – 5000 | 15 |
| 5000 – 6000 | 5 |
| Total | 600 |
Compute the median income.
Solution
| Weekly income (in Rs) |
Number of families `(bb(f_i))` |
Cumulative frequency (cf) |
| 0 – 1000 | 250 | 250 |
| 1000 – 2000 | 190 | 250 + 190 = 400 |
| 2000 – 3000 | 100 | 440 + 100 = 540 |
| 3000 – 4000 | 40 | 540 + 40 = 580 |
| 4000 – 5000 | 15 | 580 + 15 = 595 |
| 5000 – 6000 | 5 | 595 + 5 = 600 |
According to the question,
n = 600
∴ `n/2 = 600/2 = 300`
Cumulative frequency 440 lies in the interval 1000 – 2000.
Hence, lower median class, l = 1000
f = 190,
cf = 250,
Class width, h = 1000
And total observation n = 600
∴ Median = `l + ((n/2 - cf))/f xx h`
= `1000 + ((300 - 250))/190 xx 1000`
= `1000 + 50/190 xx 1000`
= `1000 + 5000/9`
= 1000 + 263.15
= 1263.15
Hence, the median income is Rs.1263.15.
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