GMAT TIGER wrote:

bmwhype2 wrote:

A colony of bacteria doubles every morning while every evening 1000 bacteria die.

What was the original size of the colony if the colony disappeared by the end of the 3rd day?

What was the original size of the colony if the colony disappeared by the end of the 6th day?

How do i set up an algebraic approach?

1. What was the original size of the colony if the colony disappeared by the end of the 3rd day?

suppose the no of bactaria at the begaining = x

the no of bactaria next morning = 2x

2 {2 (2x - 1000) - 1000} - 1000 = 0

2 (2x - 1000) - 1000 = 1000/2

2x - 1000 = (500 + 1000)/2

x = (750 + 1000)/2

x = 875

2. What was the original size of the colony if the colony disappeared by the end of the 6th day?

suppose the no of bactaria at the begaining = x

the no of bactaria next morning = 2x

2{2(2[2 {2 (2x - 1000) - 1000} - 1000] - 1000) - 1000} - 1000 = 0

solving for x, x = 984.375