Question

On a rainy day, a shopkeeper sells two colors of umbrellas red and black. He sells not more than 20 umbrellas of each color. At least twice as many black ones are sold as the red ones. If the profit on each of the black umbrellas is Rs. 30 and that of the red ones is 40, then how many of each kind must be sold to get a maximum profit?

Answer 1

according to question
Red = R 
Black = B
Profit on one Black umbrella = 30 Rs
Thus on B   = 30 B

and 
on Red umbrella = 40 R

B = 2R
Thus
Profit on black umbrellas  = 60R
Thus      
60R + 40R = 30*20 + 40 *20
    100R = 1400
           R = 14

thus B = 7