Q1-There are 5 girls and 6 boys .How many arrangements can be made if all the girls must at odd places in a row?

So basically what you want to do is place the boys first

_B_ B_B_B_B_B_

The _''s represent where the girls are to be placed.

therefore no of ways is 

7P5

since there are 7 spots and 5 girls to be permuted.

Hope this helped!