# A very stupid question, calculation problem

1. Jun 30, 2010

### cubejunkies

0.10 mL of oil can spread over a surface of 40 m^2 of water in a film one molecule thick to prevent the water from evaporating as fast. If one nanometer is 1 x 10^-9 meters, what is the length of one oil molecule in nanometers?

Ok so this is a really stupid question, but I got the correct number, but my decimal is in the wrong place, and ive done the problem over and over and over so theres something wrong in my calculations. The correct answer is 2.5 nanometers, but I always get 25 nanometers. Heres my thought process:

0.10 mL/ 100 cm * 0.10 mL/40 m^2/100 cm/1*10^-9 = 2.5*10^1

This is a really stupid question and I apologize

2. Jun 30, 2010

### Staff: Mentor

3. Jun 30, 2010

### cubejunkies

cm*nm/m :( i tried multiplying by (1m/100 cm) again as a fudge factor, bu then it made the answer 2.5*10^-1 obviously so idk

4. Jun 30, 2010

### Staff: Mentor

It looks to me like you are using conversion factors at random. Try to make it in a systematic way. For example - convert everything to meters (meters, squared meters and cubed meters).

5. Jun 30, 2010

### cubejunkies

okay, and since mL are cm^3 and its a monolayer of oil, could i make it into cm^2 because of that?

6. Jun 30, 2010

### Staff: Mentor

No, volume and surface are different things.