Ok, so this problem has been giving me a headache and I've been going through countless and nonsensical formulas to try to figure it out: A red blood cell has a radius of 5.0x10^-6. A large number of red blood cells are laid side by side in a line of a length of 1.5 meters. How many cells are in the line.

Question

anonymous · Answer

My first thought was to try to find the volume or area of the cell and then integrate it with the length, but nothing.

ranga · Answer

Divide the length by the diameter of the cell.

anonymous · Answer

It's implied that the measurement off the red blood cells are in micrometers, yes.

anonymous · Answer

Wow, that really worked! Thank you, ranga. I have a question though. This may sound silly, but why would you divide by the length? I understand that you need to find the diameter, but then how do you know that you are supposed to divide it?

agent0smith · Answer

They're all lying side by side. Picture it or draw it. Why would volume matter? All that matters is the length each takes up.

anonymous · Answer

Because the total length would be 
diameter of cell  *  number of cells

anonymous · Answer

So that means  number of cells = total length / diameter of cell

anonymous · Answer

Oh okay, that makes more sense. Thank you everyone. I don't understand why i needed to get so complicated with it.

ranga · Answer

You are welcome.

If you line up 100 marbles side by side and if each marble 0.5 inch in diameter, the total length will be 50 inches.