The weather reporter said it had rained 3/10" on monday, twice as much on tuesday than monday, 1/4" on wednesday, 1/2" on thursday and 2/5" on friday. what was the total rainfall for the monday through friday time period?

The answer would be 2 1/20

M- 3/10
T- 6/10 (3/10 times two)
W- 1/4
Th- 1/2
F- 2/5

To add these together, first you need to simplify:

-6/10+ 3/10 is simple because it has the same denominator (10). It would be 9/10.
-1/2 = 2/4, so 1/4+2/4= 3/4

So now we are left with 9/10+ 3/4+ 2/5

Write out all numerators above the least common denominator of 20.

18+15+8/20 = 41/20

20 goes into 41 twice with a remember of 1. So your simplified version would be 2 1/20.