A certain bacteria swims with a speed of 3.5 um/sec.How long will it take to cross the ends of petridish?

Question

A certain bacteria swims with a speed of 3.5 micrometer / second. How long will it take to cross the ends of a petri dish, if the diameter of the dish is 9cm?

Answer 1

This is a very simple algebra problem, but you have to be careful with units.

Convert 9 cm first into millimeters and then in to micrometers:

9 cm * 10 mm/cm * 1000 um/mm= 90,000 um.

Then divide by the swimming speed of the bacterium, and you've got your answer.

Answer 2

9 cm = 90 mm = 90,000 micrometers