Answer:
250 grams of the 60% cocoa bar and 150 grams of the 92% cocoa bar should be used.
Explanation:
Given that Shani has 2 chocolate bars, one that had 60% cocoa and the other that had 92% cocoa, to determine what mass of each bar must she mix to obtain 400g of chocolate with 72% cocoa, the following calculation must be performed:
100 x 0.6 + 0 x 0.92 = 60
90 x 0.6 + 10 x 0.92 = 63.2
80 x 0.6 + 20 x 0.92 = 66.4
70 x 0.6 + 30 x 0.92 = 69.6
65 x 0.6 + 35 x 0.92 = 71.2
63 x 0.6 + 37 x 0.92 = 71.84
62.5 x 0.6 + 37.5 x 0.92 = 72
400 x 0.625 = 250
Thus, 250 grams of the 60% cocoa bar and 150 grams of the 92% cocoa bar should be used.