Three-eighth of 320 chairs was sold at a profit of Tk. 50 each and the rest for Tk. 33600. If the seller makes a profit of 20% on the whole transaction, what is the cost price of each of the chair?

Question: Three-eighth of 320 chairs was sold at a profit of Tk. 50 each and the rest for Tk. 33600. If the seller makes a profit of 20% on the whole transaction, what is the cost price of each of the chair?

Solution:
Three-eighth of 320 = (320 × 3)/8 = 120

120 chairs were sold at a profit of Tk. 50 each.
Profit on these 120 chairs = 6000.

S.P. of all 320 chairs = (C.P. of 120 chairs + Profit on 120 chairs) + S.P. of 200 chairs
= (120 × C.P) + 6000 + 33600
= (120 × C.P.) + 39600

But these 320 chairs were sold at a profit of 20%.
∴ S. P. of 320 chair is = (120/100) ×(320 × C.P.) = 1.2 × 320 × C.P. = 384 × C.P.

Now,
384 × C.P = 120 × C. P. + 39600
⇒ 384 C.P. = 120 C.P. + 39600
⇒ 264 C.P. = 39600
⇒ C. P. = 150.