To find the marks Raju must get in chemistry to have an average of 80 marks across mathematics, physics, and chemistry, we can use the formula for calculating the average. The average of three subjects is given by:
\text{Average} = \frac{\text{Sum of scores in all subjects}}{\text{Number of subjects}}
We know:
- Marks in Mathematics = 75
- Marks in Physics = 85
- Required average = 80
Let the marks Raju needs in chemistry be x. Therefore, the equation for the average becomes:
\frac{75 + 85 + x}{3} = 80
Solving this equation:
75 + 85 + x = 80 \times 3
160 + x = 240
x = 240 - 160
x = 80
Therefore, Raju must score 80 in chemistry to have an average of 80 marks in all three subjects.
This matches the given correct answer, so option B, 80, is correct.
To ensure clarity:
- x = 80 ensures the sum of marks = 75 + 85 + 80 = 240, and dividing by 3 gives the average as 80.
Important Questions from Average (Notes)
- If the average of p numbers is $q^2$ and that of q numbers is $p^2$, then the average of (p + q) numbers is :
- The average of 101 consecutive odd numbers is 303. Find the largest number.
- For three consecutive years, the cost of a product were Rs. $134$ per litre, Rs.$268$ per litre and Rs.$335$ per litre respectively. If a common man spends an average of Rs. $14740$ per year on that product, then what is the average cost of that product per litre for the three years? (In Rs. - upto two decimals)
- If the average of six consecutive even numbers is 13, then the average of the next three even numbers is:
- Raju obtained 75 and 85 marks in mathematics and physics, respectively. Find the marks he must get in chemistry to have an average of 80 marks in all the three subjects.
