A merchant bought some oranges at the rate of 3 for 16 cents. He bought twice as many oranges at the rate of 4 for 21 cents. To make a profit of 20%, based on his investment, he sold them all at the rate of 3 for k cents. Find k.
Let the number of organges he first bought = N.....so the total cost of these = N (16/3)
So the number that he bought in the second instance = 2N....so the total cost of these = 2N (21/4)
And the revenue he makes = 3N(k/3)
So
1.2 [ cost of goods sold ] = total revenue
1.2 [ N (16/3) + 2N (21/4) ] = 3N(k/3) divide through by N
1.2 ( 16/3 + 2(21/4) ] = k
1.2 [ 16/3 + 21/2] = k
(6/5) [ 32 + 63 ] / 6 = k
[ 32 + 63 ] / 5 = k
95 / 5 = k
19 = k