# Handy Numbers for Various Occasions

### Mortgage Calculations

Suppose you want to know roughly how much mortgage payments will be given a fixed rate and for various amounts of principal financed. Find the rate from the table below and use the multiplier/divisor from the column for the length of your planned loan. To find the payment, divide the known principal by the divisor, to find the principal, multiply the known payment by the multiplier (the same number). Your results should be close to those given you by a lender (but I make no guarentees they will be correct so *caveat emptor*).

Interest Rate |
30 Year Loans |
15 Year Loans |
||

4.0% | 209.46 | 135.19 | ||

4.5% | 197.36 | 130.72 | ||

5.0% | 186.28 | 126.46 | ||

5.5% | 176.12 | 122.39 | ||

6.0% | 166.79 | 118.50 | ||

6.5% | 158.21 | 114.80 | ||

7.0% | 150.31 | 111.26 | ||

7.5% | 143.02 | 107.87 | ||

8.0% | 136.28 | 104.64 | ||

8.5% | 130.05 | 101.55 | ||

9.0% | 124.28 | 98.59 | ||

9.5% | 118.93 | 95.76 | ||

10.0% | 113.95 | 93.06 |

### Temperature

Converting temperatures between Celsius and Fahrenheit is quite easy. You must remember two simple facts. First, the point where the two scales cross the freezing point is different (0 for Celsius and 32 for Fahrenheit). Second, a single Celsius degree is equal to 1.8 Fahrenheit degrees. So, to convert a Celsius temperature to Fahrenheit, multiply by 1.8 and add 32. To convert a Fahrenheit temperature to Celsius, subtract 32 and divide by 1.8.

On a calculator, that's simple. It turns out that multiplying by 1.8 is something that most people can learn to do in their head, once they know a little trick. Instead of multiplying by 1.8 in a single step (tricky for most people), start by multiplying by 2 (something most people can do). Now, you want to subtract .2 of your original amount from that answer. The trick is to realize that .2 of the original is the same as the double you already calculated, divided by 10 (again, somethine most people can do in their head). An example will illustrate this well. Suppose you want to convert 20 degrees Celsius to Fahrenheit. Start by multiplying 20 by 2. The answer is 40. Now, keep that 40 in the back of your head while you also divide it by 10 (giving you 4). Subtract the 4 from the 40 and you get 36. Add the 32 degree offset to the 36 and you get your answer. 20 degrees Celsius equals 68 degrees fahrenheit.

If you find that too hard, this might be easier. The number 1.8 can also be represented as 9/5 (nine fifths). So, instead of multiplying by 1.8, simply multiply by 9, then divide by 5. In our example above, multiply 20 by 9 to get 180, then divide by 5 to get 36. Now add your 32 degree offset. If the number you are starting with is a multiple of 5, you can do the division first (so 20 / 5 = 4 and 4 * 9 = 36). To convert from Fahrenheit to Celsius, simply invert the fraction. As an example, to convert from 86 degrees Fahrenheit to Celsius, start by subtracting the 32 degree offset (86 minus 32 equals 54). Now divide by 9, giving you 6 and multiply that by 5, giving you the final answer of 30 degrees Celsius. You can multiply by five first and then divide by nine if that works out easier.

As a side note, to convert Celsius to Kelvin, simply add 273.15 degrees. There are no meaningful negative numbers on the Kelvin scale as zero Kelvin is absolute zero.