The table shows the distribution of marks scored by students in an examination. Calculate, correct to 2 decimal places, the (a) mean ; (b) standard deviation of the distribution.

Thursday, 03 April 2025

The table shows the distribution of marks scored by students in an examination. ...

Trending Questions

** Free JAMB 2025 CBT Practice **

Take Free Practice Test On 2025 JAMB UTME, Post UTME, WAEC SSCE, GCE, NECO SSCE

ClassInterval	Frequency
60 - 64	2
65 - 69	3
70 - 74	6
75 - 79	11
80 - 84	8
85 - 89	7
90 - 94	2
95 - 99	1

The table shows the distribution of marks scored by students in an examination. Calculate, correct to 2 decimal places, the
(a) mean ; (b) standard deviation of the distribution.

Explanation

ClassInterval	Freq(f)	Mid-point(x)	$f x$	$x^{2}$	$f x^{2}$
60 - 64	2	62	124	3844	7688
65 - 69	3	67	201	4489	13487
70 - 74	6	72	432	5184	31104
75 - 79	11	77	847	5929	65219
80 - 84	8	82	656	6724	53792
85 - 89	7	87	609	7569	52983
90 - 94	2	92	184	8464	16928
95 - 99	1	97	97	9409	9409
$\sum$	40		3150		250590

(a) Mean

\bar{x} = \frac{\sum f x}{\sum f}

\frac{3150}{40}

= 78.75
(b)

S D = \sqrt{\frac{\sum f x^{2}}{\sum f} - (\frac{\sum f x}{\sum f})^{2}}

\sqrt{\frac{250590}{40} - (\frac{3150}{40})^{2}}

\sqrt{6264.75 - (78.75)^{2}}

\sqrt{6264.75 - 6201.5625}

\sqrt{63.1875}

= 7.95.

Prev Current Next

STAY UPDATED
FOLLOW US ON :

Facebook

Subjects

• Accounts - Principles of Accounts

• Christian Religious Knowledge (CRK)

• Islamic Religious Knowledge (IRK)

All Views, Names, Acronyms, Trademarks, Expressed on this website are those of their respective owners. Please note that www.schoolngr.com is not affiliated with any of the institutions featured in this website. It is always recommended to visit an institutions or sources official website for more information. In the same vein, all comments placed here do not represent the opinion of schoolngr.com

Register • Login