People meet for a business lunch
6 people meet for a business lunch. Each person shakes hands once with each other person present. How many handshakes take place?
The number of his ancestors
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
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?
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