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Question
Find the unknown entries a, b, c, d, e, f in the following distribution of heights of students in a class:
| Height (in cm) |
Frequency | Cumulative frequency |
| 150 – 155 | 12 | a |
| 155 – 160 | b | 25 |
| 160 – 165 | 10 | c |
| 165 – 170 | d | 43 |
| 170 – 175 | e | 48 |
| 175 – 180 | 2 | f |
| Total | 50 |
Solution
| Height (in cm) |
Frequency | Cumulative frequency (given) |
Cumulative frequency |
| 150 – 155 | 12 | a | 12 |
| 155 – 160 | b | 25 | 12 + b |
| 160 – 165 | 10 | c | 22 + b |
| 165 – 170 | d | 43 | 22 + b + d |
| 170 – 175 | e | 48 | 22 + b + d + e |
| 175 – 180 | 2 | f | 24 + b + d + e |
| Total | 50 |
On comparing last two tables, we get
a = 12
∴ 12 + b = 25
⇒ b = 25 – 12 = 13
22 + b = c
⇒ c = 22 + 13 = 35
22 + b + d = 43
⇒ 22 + 13 + d = 43
⇒ d = 43 – 35 = 8
And 22 + b + d + e = 48
⇒ 22 + 13 + 8 + e = 48
⇒ e = 48 – 43 = 5
And 24 + b + d + e = f
⇒ 24 + 13 + 8 + 5 = f
∴ f = 50
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