1).  2 minutes.

         2).  35 degrees.

         3).  13.

    Notes
  
  1). In one minute the hot tap provides 1/6 of a bathful, and  
       the cold tap provides 1/3. So together they provide
       1/6 + 1/3 = 1/2. So time to fill bath equals 2 minutes.

  2). The cold tap provides twice as much water as the hot. So
       the temperature divides the interval 15 to 75 in the
       ratio 1:2. So temperature is 15 + 60/3 = 35 degrees.

  3). Each time water is added the strength of the whisky is
       reduced by a factor of 0.95. Now 0.9513 = 0.5133,
       and 0.9514 = 0.4877. So water may be added 13
       times before strength becomes less that 0.5. 

  1. Three married couples are to sit down for dinner at a
      circular table. In how many ways can they occupy the
      six chairs if the men and women are to sit alternately?  

  2. In how many ways can they occupy the six chairs if the
      men and women sit alternately, and no man sits next to
      his wife?

  3. Four married couples are to sit down for dinner at a
      circular table. In how many ways can they occupy the
      eight chairs if they sit alternately with no man next
      to his wife?