Let the original cost of pins per dozen be Rs. x.
Since the price reduces by Rs. 4 per dozen and 12 more pins (which is 1 dozen) can be bought for Rs. 48, the difference in the number of dozens before and after the reduction is 1.
Using the relation:
48 / (x - 4) - 48 / x = 1
Step 1: Find a common denominator:
48(x - x + 4) / [x(x - 4)] = 1
Step 2: Simplify:
192 / [x(x - 4)] = 1
Step 3: Cross-multiply:
192 = x(x - 4)
x² - 4x - 192 = 0
Step 4: Factor the quadratic:
(x - 16)(x + 12) = 0
So, x = 16 (since cost cannot be negative).
After the reduction, the cost per dozen is:
16 - 4 = 12
Final Answer: Rs. 12