## Wednesday, September 6, 2017

### Fractional part of a day

A year is defined by how long it takes a planet to make a single orbit around the sun. An Earth year is 365.2422 days. To make up for the decimal part we have a leap year every four years and skip the leap year if the number of the year is divisible by 100. This means we had leap years in 2004, 2008, 2012 and 2016, but we did not have one in 2000. What this lesson is about is to take the decimal part of this time and turn it onto hours, minutes and seconds.

Step 1. Multiply the decimal part by 24 to get the number of hours.
In this case, .2422 x 24 = 5.8128, which means 5.8128 hours.

Step 2. If there is still a decimal part, multiply it by 60 to get the number of minutes. We know know a year is 365 days, 5 hours and some number of minutes. That number is 60 x .8128 = 48.768

Step 3. If there is still a decimal part, multiply it by 60 to get the number of seconds.
We know know a year is 365 days, 5 hours, 48 minutes and some number of seconds. That number is 60 x .768 = 46.08. In these problems, it is okay to round to the nearest tenth of a second, so the final answer is 365 days, 5 hours, 48 minutes and 46.1 seconds.

Let's do another example. A year on Venus is 224.65 Earth days.

Step 1. .65 x 60 = 15.6, so the year on Venus is 224 days, 15.6 hours.

Step 2. 60 x .6 = 36, so that makes the year on Venus 224 days, 15 hours and 36 minutes. There is no more decimal part, so we don't have to add any seconds to our answer.

Here are two more practice problems. The answers are in the comments.

1. It takes Mercury 87.969 Earth days to travel around the sun. Write this number in days, hours, minutes and seconds.

2. It takes Mars 686.98 Earth days to travel around the sun. Write this number in days, hours, minutes and seconds.

## Tuesday, July 18, 2017

### Notes for Homework 8, duy Wed. July 19

A quick reminder: this homework will not be accepted late because the answer sheet will be given out at the end of class to help study for Thursday's midterm.

Notes on scientific notation

Notes on Set Theory

Notes on Venn Diagrams

Notes on contingency tables and probabilities

## Sunday, February 19, 2017

### Notes for Homework 4, due Wed. Feb. 22

Because of the Monday holiday, homework is due on Wednesday. There will be no quiz this week.

Notes on the Richter scale and bels and decibels, abbreviated B and dB.

Notes on square roots and the Pythagorean Theorem.