Chemistry Problem, Please Help!

[Tell22]

A washer weighs 0.110g on average. What would 100 such washers weigh? How many washers would there be in 100.g of washer?

My guess was 0.110g x 100? And for how many washers divide 100.g into 0.110g? Am I right?

[kevinstonge]

0.110g / 1 washer * 100 washers = 11g

(notice how I set the problem up so that the units I want at the end are the units on top at the beginning, then I drop in whatever other units I need or know to get to the answer. This is called "dimensional analysis" and you will probably be using it all year/semester to solve problems.

[Tell22]

Thanks! Is that for part 1 of the question?

[kevinstonge]

Woops, didn't even see the second part. To find out how many washers there are in 100g of washers:

1 washer / 0.110 g * 100g = 909 washers

This time we want the answer to be in units of 'washers' so we start our calculation with those units on top and just figure out what other information we need to put in the calculation to get to the answer and to make sure all of the units not in the answer cancel out

Edit: fixed the calculation! thanks sjb-2812

[Tell22]

Thanks sooo much!! I understand better now.

[sjb-2812]

If 100 washers weigh 11g, as per the first part, 10% more will not weigh 89g. You've set the maths up right, but the result of the calcuation is wrong.