OKAY !!! 7 days in a week ... we have to choose 3 days from 7 days and that can be done in $7\choose 3$ ways.

But those arrangements are not feasible where 3 days are consecutive. How many such choices are there?

We are choosing 3 objects from 7 objects where all three are together. Let's assume that these three are only one object. then we are choosing 1 object from 5 objects which can be done in 5 ways. and these 3 can be arranged in $3!$ ways.

Hence, Number of choices not feasible are : $6\times 5=30$

Hence number of possible choices are = ${7 \choose 3 }-30 = 35$