Cereal A is 10% sugar by weight, whereas healthier but less delicious Cereal B is 4% sugar by weight. To make a delicious and healthy mixture that is 5% sugar, what should be the ratio of Cereal A to Cereal B, by weight?
Options
A) 2 : 9 B) 2 : 7 C) 1 : 6 D) 1 : 4 E) 1 : 5

Rationale: "ratio of a / ratio of b = ( average wt of mixture - wt of b ) / ( wt of a - average wt of mixture ) = > ratio of a / ratio of b = ( 5 - 4 ) / ( 10 - 5 ) = 1 / 5 so they should be mixed in the ratio 1 : 5 answer - e"
Answer: E