Assuming that the medication comes in 10ml vials, calculate the days' supply for a prescription written as Humalog U-100 Inject 10 U SQ QID.

Humalog U-100 is a 10 ml bottle that has 100U/ml. The days' supply is calculated this way:
Units in 1 bottle = 100 U/1ml = x U/ 10ml
Cross multiply and:
x = 1000 U
To solve for days supply of prescription:
40 U/ 1 day = 1000 U/ x day
Cross multiply and:
x = 25