Thanks for the links.

Another Mixture Problem

Coffee World blends two types of coffee, putting in 2 parts of a 33 cent a pound grade to 1 part of a 24 cent a pound grade. If the mixture is changed to 1 part of a 33 cent a pound grade to 1 part a 24 cent a pound grade ,how much will Coffee World save in blending 100 pounds? a) $0.90 b) $1.00 c) ...

i didn't understand the explanation

Outstanding performance...You do own the gmat!

Interest problem

If money is invested at r percent interest,compounded annually,the amount of investment will double in approximately 70/r years. If Pat's parents invested $ 5000 in a long term bond that pays 8 percent interest,compounded annually, what will be the approximate total amount of investment 18 years lat...

Percentage problem

A store charges $28 for a certain type of sweater. This price is 40% more than the amount it costs the store to buy one of these sweaters. At end of season sale, store employee can purchase any remaining sweaters at 30% off the store's cost. How much would it cost an employee to purchase a sweater o...

Population Problem

A certain population of bacteria doubles every 10 minutes. If the number of bacteria in the population was intially was 10^4.What was the number in the population 1 hour later?

A.2(10)^4
B.6(10^4)
C.(2^6)(10^4)
D.(10^6)(10^4)
E.(10^4)^6

(x+y)^2-(x-y)^2=a^2-b^2
x^2+2xy+y^2-x^2+2xy-Y^2=a^2-b^2
4xy=a^2-b^2
2xy=(a^2-b^2)/2