Calculating Sixth Subject Marks Using Average

The problem asks us to find the marks obtained in the sixth subject, given the marks in five subjects and the average marks across six subjects. We can solve this using the definition of average.

Identify Given Information

• Marks in 5 subjects: 91, 86, 81, 79, 92
• Total number of subjects: 6
• Average marks in 6 subjects: 85

Understand the Average Formula

The average is calculated by dividing the sum of all values by the count of values. In this case:

$Average Marks = (Sum of Marks in all 6 Subjects) / 6$

We can rearrange this formula to find the total sum of marks:

$Sum of Marks in all 6 Subjects = Average Marks × 6$

Calculate Total Marks for Six Subjects

Using the given average marks of 85 for 6 subjects:

Sum of Marks = $85 \times 6 = 510$

Calculate Sum of Marks for Five Subjects

Add the marks received in the five known subjects:

Sum of 5 Subjects = $91 + 86 + 81 + 79 + 92$

Sum of 5 Subjects = $429$

Determine Marks in the Sixth Subject

Subtract the sum of marks from the five subjects from the total sum of marks for all six subjects:

Marks in 6th Subject = (Sum of Marks in all 6 Subjects) - (Sum of Marks in 5 Subjects)

Marks in 6th Subject = $510 - 429$

Marks in 6th Subject = $81$

Therefore, the student received 81 marks in the sixth subject.