question_answer

For the month of February, a class teacher of Class IX has the following absentee record for 45 students- Find the mean number of days, a student was absent.
Number of days of absent	0 ? 4	4 ? 8	8 ? 12	12 ? 16	16 ? 20	20 ?  24
Number of students	18	3	6	2	0	1

Answer:

C.I.	\[{{f}_{i}}\]	\[{{x}_{i}}(mid-value)\]	\[d={{x}_{i}}-A\]	\[{{f}_{i}}\times {{d}_{i}}\]
0 ? 4	18	2	\[12\]	\[216\]
4 ? 8	3	6	\[8\]	\[24\]
8 ? 12	6	10	\[4\]	\[24\]
12 ? 16	2	A=14	0	00
16 ? 20	0	18	4	00
20 ? 24	1	22	8	08
	\[\sum{{{f}_{i}}=30}\]			\[\sum{{{f}_{i}}{{d}_{i}}=-256}\]
\[Mean=A+\frac{\sum{{{f}_{i}}{{d}_{i}}}}{\sum{{{f}_{i}}}}\]
\[=14+\left( \frac{-256}{30} \right)\]
\[=14-8.53\]
\[=5.47\]