A medicine has 60% substance S and 40% substance T. If the cost price of S is increased from Rs. 30 to Rs. 40 per unit and the cost price of T is decreased to Rs. 20 from Rs. 30 per unit, then the cost of the medicine will _____ by _____%.

Correct option is D

Given:

Medicine mixture: 60% substance S, 40% substance T

Initial cost of S = Rs. 30 per unit → Increased to Rs. 40 per unit

Initial cost of T = Rs. 30 per unit → Decreased to Rs. 20 per unit

Formula Used:

% Change = $$\frac{\text{New Cost} - \text{Initial Cost}}{\text{Initial Cost}} \times 100$$​​

Solution:

Initial cost = (0.6 × 30) + (0.4 × 30) = 18 + 12 = Rs. 30 per unit

New cost = (0.6 × 40) + (0.4 × 20) = 24 + 8 = Rs. 32 per unit

Percentage change = $$\frac{32 - 30}{30} \times 100$$​​

= $$\frac{2}{30} \times 100$$​​

= 6.67%

Thus, The cost of the medicine will increase by 6.67%