Do Now

• How many sig figs are in the following numbers and what is their precision:

• 34.20 g• 20.0 m• .0032 km• .2003 g

Todays Goal

• Become experts at rounding math problems to the correct precision/sig figs

• Homework:(before the class after next)• Finish Rounding Homework• Read notes 11-12 and watch the video on

scientific notation before day 6 (1.04 notation)

What is precision?

• Is 7.0 cm the same thing as 7.00 cm?

Is 7.0 cm the same thing as 7.00 cm?

• No, and here is why;• Think back to the measurement lab. The

precision of your measurement depended on the tool you were using

VS

VS7.0 cm 7.00 cm

Why is precision important?

• Comes into play when you need to do math• For example;– If you added 11 km and .003 km you may be tempted to put 11.003 km as the answer

• THIS WOULD BE WRONG!

Why?

• 11km is only precise to the kilometer. It could actually be 11.427 km (or some other measurement) but the instruments could not read that precise.

• 11.???????, don’t know what those numbers are!

Why?

• If you put your answer as 11.003 km you are saying that all your measurements were precise to the thousandths place (WHICH THEY WEREN’T!)

So what is 11km +.003km?

• To answer that, you will have to do some rounding

• You always want to round to the least precise measurement place when adding/subtracting

• “WHEN ADDING OR SUBTRACTING NUMBERS, RIGHT THERE IN YOUR FACE LOOK FOR THE ONE THAT’S LEAST PRECISE AND ROUND IT TO THAT PLACE!”

11km + .003 km

• Least precise place is the ones place, so we will round to the ones.

• 11km + .003 km = 11.003 km 11 km

Look in your packet

Look in your packet

Examples in the notes

• A) take a look, what is the least precise number there?– Tenths– Final measurement is rounded to the tenth

• B) thousandths • C) Hundreds

What if we multiply/divide?

• IF YOU HAVE SOME MEASUREMENTS TO MULTIPLY OR DIVIDE, ROUND TO THE FEWEST SIG FIGS, COUNTING FROM THE LEFTWARDS SIDE!

• In other words, you want to keep the lowest number of sig figs.

Examples in your packet

Examples in your packet

Another example

Practice

• 20.1 g + 60.33 g = 60.43 g After rounding• 60.4 g• 170 ml - 17.0 ml = 153.0 ml after rounding• 150 ml• 17g/ml x 5ml = 85 g after rounding• 90g• 2134g / 17.6ml = 121.25 g/ml rounding• 121g/ml

Rounding homework

• Get started on it! • Run into trouble?– Ask a neighbor (they’re closer after all)– Ask me!

• When your finished, have me check it• HW: Read notes 11-12 and watch the video

on scientific notation before day 6 (1.04 notation)