i need someone to check my work?

Question

sorry, my teacher is lame and doesnt give us answers to our homwork after he has checked it. I have a test tommaroow and am not sure if my answers are correct...

1. (0.0423)(2.909)(4.4*10^8)=?

i got 5.5 * 10^7

needs to have 2 sig figs in answer.

2. 27.32 + 28.444 + 28.2=

i got 83.964.

but the final answer needs to have 3 sig figs so i got 84.1?

3. (4.9211)(0.0443) / [(0.000934)(2.892 *10^-7)]

i got 80.7 * 10^-7

the answer needs tohave 3 sig figs.

To all questions that may apply:
if not correct, pelase explain.
thank you!

can you elaborate joey d? your last answer really helped thanks.

Answer 1

1. INCORRECT
When you do the math, you get
54,142,308
Since 4.4 only has 2 sig figs (the lowest), you have to round that answer to 2 sig figs.
It would round to
55,000,000 (2 sig figs)
and that would be
5.5 * 10^7

2. INCORRECT
When you do the math before rounding, you get 83.964
Since 28.2 only has 3 sig figs (lowest) you have to round your answer to 3 sig figs. You round the 9 to 0 and the 3 to 4 and the answer becomes
84.0 (the .0 is important!, don't forget it)

3. CORRECT

Answer 2

Use a TI 85 calculator I think it is...how could three sig figs be 84.1 for 83.964 ---not rounded properly

Answer 3

yup they all look right except for #2
I was taught w/ sig figs that when adding you add columns.
so... (if you added)
27.320
28.444
28.200
-----------
83.9 because where the zeros are are uncertian digits aka you don't know that they are 0s
so you have to eliminate those whole columns in order to do the problem, it would look something like this
27.3
28.4
28.2
-------
83.9


all the others look right!
good job!
you might want to check the way your teacher does add or sub sig figs.
good luck

Answer 4

Do you know how to use a calculator and do you know the order of operations Check you work with a calculator.