Python does the arithmetic you know: +, -, *, /, and ** for powers. Two more are handy at work: // divides and rounds down to a whole number, and % gives the remainder. 135 // 60 is 2 and 135 % 60 is 15, so 135 minutes is 2 hours and 15 minutes.
/ always gives a float, even when it divides evenly: 10 / 2 is 5.0.
Python follows the usual order: powers first, then * and /, then + and -. Add parentheses when you mean something else, as in percent change: (new - old) / old * 100.
round(x, 2) rounds to two decimal places. Round at the end, not halfway through, so small errors don't add up. One surprise: round(2.5) is 2, because Python rounds halves to the even number.
Floats are close approximations, so 0.1 + 0.2 shows 0.30000000000000004. Rounding for display takes care of it.