For The Mathematically Inclined

What is the minimum number of squares to be colored red in a 10X10 grid so that any L-shaped figure consisting of 4 unit squares of the grid contains at least 2 red squares?

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Problems from 08/17/17

Problem 1:

The original price of a car is $30000. The manufacturer offers a $4000 rebate. The dealer gives an additional 20% discount. What is the final price of the car?

Solution 1
$20,800

Problem 2:

In a new scheme, the dealer if offering 20% discount on car plus additional discount for collective buying. The collective buying discount works as follows for a group of 10 everyone gets additional 10% discount, a group of 100 get 10% on top, and a group of 1000 get additional 10%, and so on. What should be the size of the group to get 50% discount on the car?

Solution 2
100,000

Congratulations to Ramachandran Balakrishna and Keshiv Tandon, who were the winners of the last set of puzzles.