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Find the probability that a student selected at random from the class scored:

Given the marks scored by 40 students in an objective test out of 40:

\begin{tabular}{|l|c|c|c|c|c|c|c|c|}
\hline
Marks scored & 3 & 8 & 13 & 18 & 23 & 28 & 33 & 38 \\
\hline
No. of Students & 2 & 5 & 9 & 6 & 3 & 4 & 5 & 1 \\
\hline
\end{tabular}

a) Marks greater than 28

b) Marks less than 28

c) 33 marks

d) Between 3 and 33 marks


Sagot :

Let's start by extracting and understanding the given data from the table. The table indicates the number of students who scored specific marks:

[tex]\[ \begin{array}{|c|c|c|c|c|c|c|c|c|} \hline \text{Marks scored} & 3 & 8 & 13 & 18 & 23 & 28 & 33 & 38 \\ \hline \text{No. of Students} & 2 & 5 & 9 & 6 & 3 & 4 & 5 & 1 \\ \hline \end{array} \][/tex]

Total number of students:
[tex]\[ 2 + 5 + 9 + 6 + 3 + 4 + 5 + 1 = 35 \][/tex]

Let's calculate the probabilities for each part:

a) Marks greater than 28:

Students who scored greater than 28 are those who scored 33 or 38. The number of such students is [tex]\(5 + 1 = 6\)[/tex].

Probability (P) is given by:
[tex]\[ \text{P(marks > 28)} = \frac{\text{Number of students who scored more than 28}}{\text{Total number of students}} = \frac{6}{35} \approx 0.1714 \][/tex]

b) Marks less than 28:

Students who scored less than 28 are those who scored 3, 8, 13, 18, or 23. The number of such students is [tex]\(2 + 5 + 9 + 6 + 3 = 25\)[/tex].

Probability (P) is given by:
[tex]\[ \text{P(marks < 28)} = \frac{\text{Number of students who scored less than 28}}{\text{Total number of students}} = \frac{25}{35} \approx 0.7143 \][/tex]

c) Scored 33 marks:

The number of students who scored exactly 33 marks is [tex]\(5\)[/tex].

Probability (P) is given by:
[tex]\[ \text{P(marks = 33)} = \frac{\text{Number of students who scored 33}}{\text{Total number of students}} = \frac{5}{35} \approx 0.1429 \][/tex]

d) Between 3 and 33 marks (inclusive):

Students who scored between 3 and 33 marks include those who scored 3, 8, 13, 18, 23, 28, and 33. The number of such students is [tex]\(2 + 5 + 9 + 6 + 3 + 4 + 5 = 34\)[/tex].

Probability (P) is given by:
[tex]\[ \text{P(3 ≤ marks ≤ 33)} = \frac{\text{Number of students who scored between 3 and 33 (inclusive)}}{\text{Total number of students}} = \frac{34}{35} \approx 0.9714 \][/tex]

In summary, the probabilities are:
a) [tex]\( \approx 0.1714 \)[/tex]
b) [tex]\( \approx 0.7143 \)[/tex]
c) [tex]\( \approx 0.1429 \)[/tex]
d) [tex]\( \approx 0.9714 \)[/tex]