Odd ball out

You are given 10 baskets. 9 of the baskets each have 10 balls weighing
10kg per ball, however one basket has 10 balls weighing 9kg each. All
the balls and baskets are identical in appearance. You are asked to
determine which basket contains the 9kg balls. You have a suitable
scale, but may only take a single measurement. No other measurements may
be taken (like trying to determine by hand). You may remove balls from
the baskets but may still only take one measurement.
1. How do you do it?
2.Now if two balls are defective, how do you do it in only one weighing?

Answer:

1. use, ∑n principle , i.e (∑10 - actual wieight)^th basket has defective balls.
2. (Possible answer) Use ∑n² principle and (∑n² - actual weight)=diff should be divided into two variables a, b such that , a²+b² = diff, and a^th and b^th baskets are defective.