A pharmacist needs 16 liters of a 4% saline solution. He has a 1% solution and a 5% solution available. How many liters of the 1% solution and how many liters of the 5% solution should he mix to make the 4% solution?

x = liters of 1% solution

y = liters of 5% solution

x + y = 16

0.01x + 0.05y = 0.04*16 = 0.64

y = 16 - x

0.01x + 0.05(16 - x) = 0.64

0.01x + 0.8 - 0.05x = 0.64

0.16 = 0.04x

x = 4

y = 12

Her conclusion that 90% of the student body wants the colors changed is an INCORRECT conclusion. The 90% out of 100% is not referring to the total numbers of the student body.For example, 100 people are members of student body if only 50 members responded the survey, then we have:
 90% of 50 members who answered the survey said that they want the changed.