Math word problem?

Let the number of litres of 60% solution be x.

When you mix those x litres with the 50 litres, you have

x + 50 litres.

Therefore:

60%*x + 90%*50 = 70%*(x + 50)

0.6x + 0.9*50 = (x + 50)0.7.

You need only the one equation.

Solve that for x, and you have the number of litres.

let x = amount of 60% solution added. The new solution will be 70% and will have 50*.9+x*.6 solute. The total volume of the solution will be 50+x. So...

(45+.6*x)/(50+x) = .7

45+.6x = 35+.7x

x = 100.

100 liters

I solved this problem using an easier method, a chart.

Set it up like this:

Liters | % | Product of Liters & % (litres X %)

__x___.6___.6x

_50__.9____45

Then you add the products of that chart together (.6x and 45) and you know it must equal a final solution that has 70% (.7) of your total amount of liters. So:

.6x + 45 = .7(x +50)

10 = .1x

x = 100

Therefore the amount of liters is 100

.6x + .9 * 50 = .7 * (x + 50), where x = liters of the 60% soln.

.6x + 45 = .7x + 35, or 10 = .1x, x = 100 liters

x= the number of liters of 60% solution

50(.9)+x(.6)=(50+x)(.7)

Solving for x:

45+.6x=35+.7x

10=.1x

100=x

100 liters of 60% solution are required.

Hope this helps,

Lorax