highschool algebra problems! what the!

[voidflux]

Hello everyone, I just discovered I need some major refreshing on algebra, i'm struggling with basic word problems! So I need to double check to make sure i'm doing this right...
okay problem #1:

I need to find the weighted average of four test scores. This seems very basic, but i forgot how to find it!! I know how to find a regular average, add the test scores then divide by the # of tests. But this is somthign different i think, an example would be:

75 .20
95 .35
85 .15
65 .30

do they want me to simply do this?
wAverage = [(.20+.35+.15+.30)]/(4)
?

okay problem #2:

A sales person leaves his home every Monday and returns every Friday. He travels by company car. Each day on the road, the salesperson records the amount of gasoline put in the car. Given the starting odometer reading(that is, the odometer readinbg before he leaves on monday) and the ending odometer reading (the odometer reading after he returns home on friday). here some sample data:
start: 68723
end: 71289
Mon: 15.75
Tues: 16.30
Wed: 10.95
Thru: 20.65
Fri: 30.00

So I figured I wanted to find the change in distance, so i subtracted final distance from orginal, and got change in distance = 2566 miles.
Then I figured i would need to find the average gals of gas entered each day so i added up Mon-Fri and divided by 5 and got 18.73. So i took 2566 miles/18.73gals and got 137 miles/gal? this isn't right at all! I think its because the input is 15.75, etc, i think thats currency not gals, how would u know the answer to this if you don't know how much money per gallon they sell? Am i missing somthing here? Thanks for listening to my lack of knowledge.

[sql_lall]

OK:
1) you will notice that .20 + .35 + .15 + .30 = 1
So, it looks to me like these are percentages.
So, to find the weighted average, its just 75*.2 + 95*.35 + 85*.15 + 65*.3 = 80.5

2) "i added up Mon-Fri and divided by 5"
in this case you don't divide by 5.
2566=TOTAL miles
=> to find miles/gals you need
TOTAL miles/ TOTAL gallons
=> don't divide by 5, as you do want the total amount of fuel, not the average.

[voidflux]

Thanks!