Charles owed $390 to his friend. on the first day charles paid his friend $12. each following week the amount charles paid his friend increased by the same amount. after 10 payments, charles had paid back the full amount. by how much did each payment increase?

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?

Acredit card advertises an annual interest rate of 23%. what is the equivalent monthly interest rate?

What value is a discontinuity of x squared plus 8 x plus 4, all over x squared minus x minus 6?