Explanation:
x = ml of the 60% solution
y = ml of the 45% solution
x + y = 600
and therefore
x = 600 - y
0.6x + 0.45y = 0.5×600
we use the above identity in this equation :
0.6(600 - y) + 0.45y = 300
360 - 0.6y + 0.45y = 300
60 - 0.15y = 0
60 = 0.15y
y = 400 ml
x = 600 - y = 600 - 400 = 200 ml