False Position

 Problem: At the end of the week a farmer has a total amount of 100 pounds of grain. The farmer started the week with an unknown quantity of grain and sold a third of that quantity. What quantity of grain did the farmer start the week with? 

Try x=75

75-(75/3)=50

Since we need the answer to be 100, which is twice as big as 50, x must then be 2 times larger than the trial number 75(75x2=150).

Thus if x=150

150(150/3)=100

Therefore the farmer started the week with 150 pounds of grain.