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

#3**+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**+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**+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**+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