Make 2 equations:-
let x be volume of 15% and y the volume of the 30% solution
x + y = 50
0.15x + 0.30y = 50*0.2 = 10
from first equation y = 50 - x, so:-
0.15x + 0.30(50 - x) = 10
0.15x + 15 - 0.30x = 10
5 = 0.15x
x = 5 / 0.15 = 33.33 mls
and y = 50 - 33.33 = 16.67 mls
Answer: she needs 33.33 mls of the 15% solution ans 16.67 of the 30%.
