how do you solve for x where x/(10000+x)=37.5%

37.5% can also be written as 375/1000. If we write it that way the equation becomes,

x/(10000+x)=375/1000

Then we cross multiply,

x/(10000+x)=375/1000 (1000)(x)=(375)(10000+x) 1000x=3750000+375x

Subtract 375x from both sides,

1000x=3750000+375x 625x=3750000

Then divide both sides by 625 to solve for x getting x=6000. Hope that helped.

Dear Cyphersum - that helped so much! Thank you!!