If you flip a penny, nickel, dime, and quarter, how many ways can you get exactly 2 tails?

Hector and alex traded video games. alex gave hector one fourth of his video games in exchange for 6 video games. then he sold 3 video games and gave 2 video games to his brother. alex ended up with 16 video games. how many video games did alex have when he started?

The radius of the earth is two times the radius of the moon. what fraction of the volume of the earth is the volume of the moon?

Angles r and s are complementary. the measure of angle r is 31 degrees. which equation can be used to find angle s?