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Mr. Butler is filling planter boxes with soil.  He has soil that is 30% sand, and he buys 9 pounds of a commercial potting soil that is 18% sand.  He mixes some of his soil with the 9 pounds of commercial potting soil.  The resulting soil mixture is 21% sand.  How many pounds of his soil did Mr. Butler use?

ForensicGirl  Feb 22, 2017

Best Answer 

 #3
avatar+12561 
+5

Soil sand content =   x * 30% = .3x

Commercial soil sand content = 9 x 18% = 1.62 pounds

 

resulting mixture is  (x+9) * 21%

 

added together must equal what is put in

.3x + 1.62 = .21 (x+9)

.3x + 1.62 = .21x + 1.89

.09x = .27

x= 3    pounds

ElectricPavlov  Feb 23, 2017
 #1
avatar
+5

Let the amount of Mr. Butler's 30% sand =S

0.30S + 0.18(9) =0.21(9+S)

0.30S + 1.62     =1.89 + 0.21S

0.30S - 0.21S =1.89 - 1.62

0.09S =0.27

S =0.27 / 0.09

S = 3 pounds - of 30% sand that Mr. Butler used.

Guest Feb 23, 2017
 #2
avatar+16 
+5

That's what we had.... I should really start learning to trust my gut.  Thank you so much for your expedient reply

ForensicGirl  Feb 23, 2017
 #3
avatar+12561 
+5
Best Answer

Soil sand content =   x * 30% = .3x

Commercial soil sand content = 9 x 18% = 1.62 pounds

 

resulting mixture is  (x+9) * 21%

 

added together must equal what is put in

.3x + 1.62 = .21 (x+9)

.3x + 1.62 = .21x + 1.89

.09x = .27

x= 3    pounds

ElectricPavlov  Feb 23, 2017

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