Question

1. The average marks of a class of 36 students in an examination are 68. If the marks of
three students were misread as 32, 45 and 56 in lieu of actual marks 56, 69 and 80
respectively, then what would be the correct average? *​

Answer 1

Let's understand the Question first :-

First Condition :-

Here, it is mentioned that the average marks of 36 students in an examination are 68 and out of 36 students 3 students got 32 , 45 and 56 marks but that marks they got were misread

Second Condition :-

The actual marks of those three students is 56 , 69 and 80 . now, we have to find the correct average marks?

Solution :-

The average marks of a class of 36 students in an examination are 68

Three students were marks were misread as 32 , 45 and 56

Let the marks of 33 students be x

Therefore,

By using mean formula, we get

Mean = Sum of observation / total observations

x + 32 + 45 + 56 / 36 = 68

x + 133 = 68 * 36

x + 133 = 2448

x = 2248 - 133

x = 2315

Thus, the sum of observations of 33 students is 2315 .

Now,

The actual marks got by those three students 56 , 69 and 80

Therefore,

By using mean formula we get :-

Mean = Sum of observations / Total observations

Subsitutes the required values:-

= 2315 + 56 + 69 + 80 / 36

= 2520/36

= 70

Hence, The actual mean is 70 $.$

Answer 2

Answer:

i) as per the table students obtained marks equal to 7 or more than equal to 7 are 5+4+3=12

hence, 12 students obtained marks equal to or more than equal to 7.

ii) as per the table students obtained marks below 4 are 2+3+3=8

hence, 8 students have obtained marks below 4.