SOLUTION: David and Moira are trying to bake a chocolate cake for Alexis’ birthday. They require 300g of
chocolate that is 86% cocoa. Johnny has two types of chocolate: one that is 80% co
Question 1175937: David and Moira are trying to bake a chocolate cake for Alexis’ birthday. They require 300g of
chocolate that is 86% cocoa. Johnny has two types of chocolate: one that is 80% cocoa and
another that is 90% cocoa. What is the quantity of each type of chocolate that David and Moira
need to use to make Alexis’ birthday cake? Answer by ikleyn(52855) (Show Source):
Let x = amount (the mass in grams) of the 90% cocoa.
Then the mass of the 80% cocoa is (300-x) grams.
After that, write the standard equation of conservation mass (the pure cocoa)
in the mixture before and after the mixing
0.9x + 0.8(300-x) = 0.86*300.
From this equation
x = = 180.
ANSWER. 180 grams of the 90% cocoa and the rest, (300-180) = 120 grams of the 80% cocoa.
CHECK. I will check the concentration = 0.86 = 86%. ! Precisely correct !
Solved.
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