21. Bob was paddling his canoe upstream at at constant rate. After six
miles, the wind blew his hat into the stream. Thinking that he had no chance to recover his hat, he continued upstream for six more miles before
turning back. he continued rowing at the same rate on his return trip and overtook his hat at exactly the same spot where he began his journey eight hours
earlier. What was the velocity of the stream?

1 MPH. Bob was rowing at a constant rate in relation to the water, and it took him eight hours to travel 24 miles. At the point where he lost his hat, he had been rowing for six miles, or two hours. To meet Bob where he began his journey, the hat had to travel downstream six miles. Bob didn't reach the hat until after he had rowed the remaining 18 miles, or for six more hours. Thus, it took the hat six hours to travel six miles, carried by the stream velocity of 1 MPH.

22. What number is missing from the following series?

31, 62, 93, 25, 56, ?

87. These are multiples of 13 with reverse digits: 13, 26, 39, 52, 65, 78.

23. The math department was making arrangements for a farewell luncheon to honor
one of their retiring colleagues. They calculated that it would cost each person $30. "It's lucky that there aren't five fewer of us to split
the bill, or it would be $10 more each", said one of the math teachers. How many people would be splitting the bill, and how much did
the luncheon cost?

Twenty people split a $600 dollar bill.

24. Meditate on the number 123. Now complete the following sequence:

116, 125, 206, 224, 305, ?

The missing number is 314. Rearrange the digits 123 in every possible way (123, 132, 213, 231, 312, 321), and then subtract 7 from each result to get the series.

25. In this little multiplication sum the five letters represent different
digits. What are the actual figures? There are no zeros involved.

S E A M

__
T__

M E A T S

26. John was trying to take a short cut through a very narrow tunnel when he
heard the whistle of an approaching train behind him. Having reached three-eighths of the length of the tunnel, he could have turned back and cleared
the entrance of the tunnel running at 10 miles per hour just as the train entered. Alternatively, if he kept running forward, the train would reach him
the moment he would jump clear of the tracks (at the exit.) At what speed was the train moving?

At 40 miles per hour. The train would enter the tunnel when John was still two-eighths from the exit or a quarter of the tunnels length. If the train was to reach him at the exit, it would have to travel at four times Johns speed, i.e. 40 miles per hour.

27. Ten years ago, a man was offered a motorcycle for $1024, but he declined to buy it.
A year later, he was offered the same motorcycle for $640, but again decided not to buy it. A little while after that, he was again offered the motorcycle for $400. Again,
he declined to buy it. Last week, he declined to buy the motorcycle again, even though it was now offered for $250. If the owner offers it for sale yet again, and he
makes a consistent reduction of the price, how much will it be the next time he offers it for sale?

Each price was 5/8 of the previous price. So the next price will be $156.25.

28. Susan is now four-fifths of her sister Jane's age. Three years ago, she
was one-half her sister's age. Five years from now, Susan will be nine-tenths of Jane's age. If they are both under the age of ten, how old
are they now?

Susan is 4 and Jane is 5.

29. Of three sisters named April, May, and June, none is yet twenty-one.
April is now as old as June was fourteen years ago, and two-thirds of May's age. May, on the other hand, will be June's age when May is twice as old
as she is now plus two years. Three years ago, May was as old as April is now. How old are April, May, and June?

April is six, May is nine, and June is twenty.

30. For a wedding reception, the caterer found that 6 sandwich makers made 36
sandwiches in two hours. But, the caterer needs 216 sandwiches. How many sandwich makers does he need to make 216 sandwiches in one hour?

72. Each sandwich maker can make 3 sandwiches in one hour.