Final answer:
To calculate how many kgs of variety-1 rice should be mixed with the variety-2 rice, we need to consider the cost, selling price, and profit margin. By solving the equation, we find that the shopkeeper should mix 30 kgs of variety-1 rice with the 25 kgs of variety-2 rice. This will enable the shopkeeper to make a profit of 25% on selling the mixture at Rs.40/kg.
Step-by-step explanation:
To calculate how many kgs of variety-1 rice should be mixed with the variety-2 rice, we need to consider the cost, selling price, and profit margin.
Let's assume x kgs of variety-1 rice are mixed with 25 kgs of variety-2 rice to get the mixture.
The cost of the variety-1 rice is Rs.42/kg and the cost of the variety-2 rice is Rs.24/kg.
The selling price of the mixture is Rs.40/kg and the profit margin is 25%.
To calculate the profit, we first need to find the total cost of the mixture. The cost of variety-1 rice is Rs.42/kg, so the cost of x kgs of variety-1 rice is 42x Rs. since the cost of variety-2 rice is Rs.24/kg, the cost of 25 kgs of variety-2 rice is 24 x 25 = 600 Rs.
The total cost of the mixture is therefore 42x + 600 Rs.
The selling price of the mixture is Rs.40/kg, so the total selling price of the mixture is 40(x + 25) Rs.
The profit is the difference between the selling price and the cost. Therefore, the profit is (40(x + 25) - (42x + 600)) Rs.
The profit margin is 25%, which means the profit is 25% of the selling price. Therefore, (40(x + 25) - (42x + 600)) Rs. = 0.25 * 40(x + 25) Rs.
By simplifying the equation, we can solve for x, the amount of variety-1 rice to be mixed:
40(x + 25) - (42x + 600) = 0.25 * 40(x + 25)
Solving this equation will give us the value of x, which is the amount of variety-1 rice to be mixed with variety-2 rice.
Therefore, the answer is D. 30 kgs.