I'm looking at a multiple choice test here and heres one of the questions Q.) Your hair grows 5mm per week. What is its speed in m/s? I calculating everything to appropriate units and got time = 604800 seconds length = 0.005 metres then to get the rate of metres per second I divided 0.005m / 604800s and got 8 x 10-9 m/s None of the multiple choices match that answer though. The closest answer is 5 x 10-9 m/s I assume I did something wrong here but I can't see what.