Question

A prescription for 120 mL of Formaldehyde 8% with rose is brought into the pharmacy. The pharmacy has on hand Formaldehyde 37% and Formaldehyde 4% with rose. How much of each ingredient is needed to make this compound?
a. 55.5 mL of formaldehyde 37% and 80.5 mL of formaldehyde with rose
b. 14.5 mL of formaldehyde 37% and 105.5 mL of formaldehyde with rose
c. 10.1 mL of formaldehyde 37% and 55.5 mL of formaldehyde with rose

Answer 1

Use x = mL of 37% and y = mL of 4%. x + y = 120 and 37x + 4y = 8·120 = 960.

37x + 4(120 − x) = 960 → 33x = 480 → x = 480/33 ≈ 14.5 mL.
y = 120 − 14.5 ≈ 105.5 mL.

So answer b (14.5 mL of 37% and 105.5 mL of 4% with rose).