Question 98671
Let x=amount of 90/kilo needed
Then (300-x)=amount of 75/kilo coffee needed

Now we know that the value of 90/kilo coffee (90x) plus the value of the 75/kilo coffee (75(300-x)) has to equal the value of the final mixture(80)(300)).  So our equation to solve is:

90x+75(300-x)=80*300 get rid of parens

90x+22500-75x=24000 subtract 22500 from both sides

90x-75x+22500-22500=24000-22500  collect like terms

15x=1500 divide both sides by 15

x=100 kilos-------------------------amount of 90/kilo coffee needed

300-x=300-100=200 kilos---------------amount of 75/kilo coffee needed

CK

90*100+75*200=80*300
9000+15000=24000
24000=24000

Hope this helps---ptaylor