<p>A student obtains 75%, 80% and 85% in three subjects. If the marks of another subject is added, then his average cannot be less than</p>
Step-by-Step Solution
Key Concept: The average of four subjects depends on the fourth subject's marks. The minimum possible average occurs when the fourth subject has the minimum possible score (typically 0%), which gives us the lowest bound for the new average.
<p><strong>Step 1:</strong> Calculate the sum of marks in three subjects.</p><p>Sum = 75 + 80 + 85 = 240%</p><p><strong>Step 2:</strong> Let the fourth subject's marks be x%, where 0 ≤ x ≤ 100.</p><p>Average of four subjects = (240 + x)/4</p><p><strong>Step 3:</strong> Find the minimum average by considering the minimum value of x.</p><p>Minimum occurs when x = 0:</p><p>Minimum average = (240 + 0)/4 = 240/4 = 60%</p><p><strong>Step 4:</strong> Therefore, the average cannot be less than 60%.</p><p>∴ Answer: A (60%)</p>
Correct Answer: A