C is your answer by the way
First brand = A, second brand = B.
A + B = 249ml
9% A + 14% B = 13% 249ml
B = 249ml - A
9% A + 14% (249ml - A) = 13% 249ml
9A + 14 (249ml - A) = 13 * 249ml
9A + 3486ml - 14A = 3237ml
5A = 249ml
A = 49,8ml
<span>B = 249ml - A = 199,2ml
</span>
Answer: He should use 49,8ml of first brand and 199,2ml of second brand.
Also note: <span>That's an </span>approximation,<span> because </span>the volumes are not strictly additive<span>. For example: mixing 50ml pure ethanol with 50ml water will give you about 95ml of mixture. To get an accurate answer, you'd have to </span>measure<span> the volume of the final mixture and then divide your total alcohol content by </span>that<span>.</span>
<span>I think the answer would be:
B) y= 4 cos 2 theta</span>
