The number of a certain bacteria doubles in a lab culture every day. suppose there are 100 bacteria to start an experiment. write an equation for the number of bacteria n as a function of the number of days d.

The population of a bacteria culture doubles every 2 minutes. Approximately how many minutes will it take for the population to grow from 1,000 to 500,000 bacteria

Is not quite that. 
min 0 - 1,000
min 2 - 2,000=1,000*2^1
min 4 - 4000=1000*2^2; 
min 6 - 8000=1000*2^3

Be careful! It doubles every 2 minutes.

So, 1,000*2^x=500,000
2^x=500. It asks you to approx. You know that 2^9=512, so x=9.
Because the pop doubles every 2 minutes, the result=9*2=18 minutes.
hope it's perfect!