To add the probabilities, you would have to treat them like any other numbers. If they are decimals or percents, you can follow basic addition rules. If you are given the probabilities as fractions, make sure that you have common denominators when you add them.
No, because negative base sometimes results in non-real or imaginary value.
If you would like to know Mike's tax, you can calculate this using the following steps:
a market value ... 310000
the property ... 40% of the market value = 40% * 310000 = 40/100 * 310000 = 124000
the tax rate ... 145.10 per 1000 of assessed valuation
145.10 ... 1000 of assessed valuation
x ... 124000 of assessed valuation
____________________________
145.10 * 124000 = 1000 * x /1000
x = 145.10 * 124000 / 1000
x = 17992.4 (Mike's tax)
The correct result would be: Mike's tax is 17992.4.
