6 people meet for a business lunch. Each person shakes hands once with each other person present. How many handshakes take place?
A person has 2 parents 4 grandparents, 8 great-grandparents, and so on. Find the number of his ancestors during the ten generations preceding his own.
In drilling world’s deepest hole, it was found that the temperature T in degree Celsius, x km below the surface of Earth, was given by T = 30 + 25(x – 3) , 3 < x < 15. At what depth will the temperature be between 2000C and 3000C?