Question

The marks obtained by 10 students in a class are as follows, what is the probability that the average mark obtained by a student in the class is less than 70?(in decimals)

$\begin{array}{ccccc}\text{Student}& \text{English}& \text{Hindi}& \text{Mathematics}& \text{Science}\\ 1& 87& 78& 90& 89\\ 2& 90& 68& 76& 78\\ 3& 79& 68& 59& 61\\ 4& 71& 67& 79& 57\\ 5& 69& 91& 86& 76\\ 6& 87& 85& 67& 60\\ 7& 78& 90& 89& 93\\ 8& 92& 76& 88& 90\\ 9& 77& 81& 85& 86\\ 10& 86& 75& 93& 89\end{array}$

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Answer 1

$\begin{array}{cccccc}\text{Student}& \text{English}& \text{Hindi}& \text{Mathematics}& \text{Science}& \text{Average}\\ 1& 87& 78& 90& 89& 86\\ 2& 90& 68& 76& 78& 78\\ 3& 79& 68& 59& 61& 66.75\\ 4& 71& 67& 79& 57& 68.5\\ 5& 69& 91& 86& 76& 80.5\\ 6& 87& 85& 67& 60& 74.75\\ 7& 78& 90& 89& 93& 87.5\\ 8& 92& 76& 88& 90& 86.5\\ 9& 77& 81& 85& 86& 82.25\\ 10& 86& 75& 93& 89& 85.75\end{array}$

The number of students with average marks less than 70 = 2

Total number of students = 10

The probability of a student securing average mark of less than 70 $=\frac{2}{10}=0.2$