Math word problem

Question

How much water must be added to 3 gallons of a 8% insecti solution to reduce the concentration to 3%? (Water is 0% insecticid.)

Answer 1

 The concentration percent is:

 

0.08* 3 + X*0  = 0.03*(X+3)

 

0.24 = 0.03X + 0.09

 

24 = 3X + 9

 

15 = 3x

 

x=5

 

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check:

 

8% of 3 gallons is 0.24 gallons

Adding 5 gallons of water to that makes

0.24 gallons of the insecticide out of (3+5)=8 gallons

is 0.24/8 = 0.03 = 3% so yes it works.

 

 

5 gallons of water

Answer 2

Hello Olga

 

You need to first determine the volume of the 3% that will be prepared from diluting the 8% solution.  The equation to use is:

 

C_iV_i = C_fV_f

 

Rearrange to solve for V_f

 

V_f = C_iV_i / C_f = 8% x 3 gal / 3% = 8 gal

 

Volume of water to be added to the 8% solution to make the 3% solution = 8 - 3 = 5 gallons