Day 69

Algebra: Chapter 8-5, p 380

Motion Problems

Yuck – DRT problems, distance, rate and time. Rate is another word for speed or velocity. You have a rate meter in your car, its called the speedometer.

These problems are best outlined with a picture. You can use the tables in the textbook, I prefer to ALSO draw a picture so that I can grasp what the question is and what information I have.

For time problems, one person, car or plane leaving AFTER another, I (my preference) set time `t` the time of the first object leaving. The time `t` for the second event is ALWAYS NEGATIVE because time HAS PASSED or gone away. This nomenclature makes things easy for me to keep track.

The book does things the opposite way and THAT IS OK too, see example #1 for instance.

Here are some GREAT examples from too to help along. Don’t forget to check the solutions that I published on the website as well.

Math-8, Chapter 6-2, p 280

Estimating Products and Quotients

Just like we did with addition and subtraction, we estimate using rounding and compatible numbers Compatible numbers are rounded so it is easy to compute with them mentally.

For example:

`47.5 / 5.23` becomes `48 / 6` or is approximated by `8`

`8 * 98.24` becomes `8 * 100`  or about `800`


`(5/14) * (30)` becomes `(1/3) * (30)` or about `10`

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