You own 7 pairs of jeans, you want to take 2 pairs on vacation with you, how many ways can you choose 2 pairs of jeans? pls !

When you go to select the 2 pair to take ...

-- The first one can be any one of the 7 you own.  For each if these . . .
-- The second one can be any one of the remaining 6 you own.
-- So there are  (7 x 6) = 42 ways to choose 2 pairs of jeans.

But . . . . .

When you finish packing the 2 pairs of jeans you chose, it doesn't
matter which one was chosen first and which one was chosen last. 
The same jeans could have been chosen for the trip in two
different ways.

Although there are 42 ways to choose two pair, the same two pair
can be chosen in 2 different ways.  So there are only  42/2 = 21
different sets of jeans that can end up going on vacation.

First, think of what you know. you know that the number t the end of the equation will need to be subtracted because it is the money he lost from buying the lawn mower. and your first two weeks have negative profit, so that tells you that c and d are wrong. now you can plug any of the weeks into a and b to see which one works. i'll start with plugging week 1 into a.this isn't right because it says your answer for week one should be -90.so now we need to try the same thing with b.this one got you the right answer, (sometimes if you only check with one of the weeks multiple will work so you need to check with more of the weeks, but it worked out fine here)this means that b is the correct answer.let me know if you need more clarification. i hope this : )