tom and jack leave their house at the same time of 2:26. Tom is on bike , jack is on scooter. gavin sees tom every 6 min, jack every 9 min. what time will gavin see them again togather?

I'm terrible at math any here is appreciated.

Asmall (but heavy) particle placed in a glass of water will follow a zigzag motion because the particle will bounce off of the water molecules it meets. this is called brownian motion. a physicist simulates this on a computer, by varying the distance a particle can travel (called the mean free length), on average, before it collides with a water molecule and assigning the change in motion to be one of 8 directions, each with a similar probability. by running the simulated particle (with the same mean free length) many times she determines that it should take 15 seconds, on average, for the particle to fall to the bottom, with a standard deviation of 1.5 seconds. next she lets a real particle fall through a glass of water and finds that it took 18 seconds. what does she conclude, and why?

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.