A stationer buys diaries at Rs 75 per dozen and sells them at Rs 15 per piece. What is the profit in rupees on selling one dozen?

Introduction:
Compute total selling price per dozen and subtract the cost price per dozen to get profit in rupees.

Given Data / Assumptions:

• Cost price (per dozen) = Rs 75
• Selling price per piece = Rs 15

Concept / Approach:
There are 12 pieces in a dozen, so SP per dozen = 12 * 15. Profit = SP − CP.

Step-by-Step Solution:
SP per dozen = 12 * 15 = Rs 180Profit = 180 − 75 = Rs 105

Verification / Alternative check:
Profit % (optional) = 105 / 75 * 100 = 140% (not required but validates magnitude).

Why Other Options Are Wrong:
75, 100, 110: Do not match the computed difference.

Common Pitfalls:
Forgetting to convert per-piece SP into per-dozen SP.

Final Answer:
105