(i) C.P. of one pen = $\frac{50}{4}$ = ₹ 12.50.
Hence, the C.P. of one pen is ₹ 12.50.
(ii) S.P. of one pen = $\frac{80}{5}$ = ₹ 16.
Hence, the S.P. of one pen is ₹ 16.
(iii) Profit on one pen = 16 − 12.50 = ₹ 3.50.
Hence, the profit made by selling one pen is ₹ 3.50.
(iv) Profit% = $\left(\frac{\text{profit}}{\text{C.P.}} \times 100\right)$%
= $\left(\frac{3.50}{12.50} \times 100\right)$%
= $\frac{350}{12.50}$%
= 28%
Hence, the profit percent made by selling one pen is 28%.
(v) C.P. of 40 pens = 40 × 12.50 = ₹ 500.
Hence, the C.P. of 40 pens is ₹ 500.
(vi) S.P. of 40 pens = 40 × 16 = ₹ 640.
Hence, the S.P. of 40 pens is ₹ 640.
(vii) Profit on 40 pens = 640 − 500 = ₹ 140.
Hence, the profit made by selling 40 pens is ₹ 140.
(viii) Profit% = $\left(\frac{\text{profit}}{\text{C.P.}} \times 100\right)$%
= $\left(\frac{140}{500} \times 100\right)$%
= $\frac{14,000}{500}$%
= 28%
Hence, the profit percent made by selling 40 pens is 28%.
Yes, the results of parts (iv) and (viii) are the same, i.e. 28%.
Hence, the profit percent does not depend on the number of articles bought and sold; it remains the same whether it is calculated for one pen, 40 pens or 100 pens.