Problem: in what proportion must flour at $ 0.8 per pound be mixed with flour at $ 0.9 per pound so that the mixture costs $ 0.815 per pound ?
Rationale: "using weighted average method : let x be the proportion in which the $ 0.8 per pound flour is mixed with $ 0.9 per pound flour . thus 0.8 * x + 0.9 * ( 1 - x ) = 0.815 0.9 – 0.1 x = 0.815 x = 0.85 thus ratio of both flours is 6 : 1 c"
annotated_formula: divide(0.815, add(0.8, 0.9))