Katie set a goal to run 12 Miles during the school week. She ran 3.42 miles on Monday and 2.7 miles on Tuesday. How many miles does katie still need to run to reach her goal

Katie has already run a total of 3.42 + 2.7 = <<3.42+2.7=6.12>>6.12 miles.

Therefore, she still needs to run 12 - 6.12 = <<12-6.12=5.88>>5.88 miles to reach her goal. Answer: \boxed{5.88}.