Question

write an equation for the problem and solve the problem. How much 15% solution and how much 45% solution should be combined to make 30 liters of 35% solution?

Answer 1

Amount of 15% solution = 10 litres

Amount of 45% solution = 20 litres

This is based on simultaneous equations.

Let x represent the amount of the 15% solution.

Let y represent the amount of the 45% solution. Thus;

0.15x + 0.45y = 0.35(x + y) - - - (eq 1)

Since they both combine to make 30 litres solution, then;

x + y = 30 - - - (eq 2)

From eq(2), let's make x the subject to get; x = 30 - y

Putting 30 - y for x in eq 1 gives;

0.15(30 - y) + 0.45y = 0.35(30 - y + y)

4.5 - 0.15y + 0.45y = 10.5

Rearranging gives;

0.3y = 6

y = 6/0.3

y = 20 litres

Putting 20 for y in eq 2 gives;

x + 20 = 30

x = 30 - 20

x = 10 litres

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