1) 463/512
                2) John has £90, David has £30
                3) 100 ml.

    Notes

  1). Can be solved by trial and error with a calculator.
      There are 720 such fractions, but only a few need be
      tested. Alternatively, the question presents a nice
      little programming problem.
      (Several replies gave 543/612 as the answer. Check it
      out with a calculator!)

  2).     2J/3 = D + J/3
          2D/3 = J + D/3 - 80
       Solving,
             J = 90,  D = 30

  3). At 12:30 I have travelled 30 ml., so we are 220 ml.
      apart. We then approach each other at 110 mph.
      So we meet at 14:30, by which time my friend has
      covered 100 ml.

  1. What three numbers (all different) give the same result
     when multiplied together as when added together?

  2. A cube with edges 5 inches long is given a coat of paint.
     If it is then cut into 125 equal cubes, how many of these  
     will have (i) exactly three painted faces, (ii) two
     painted faces, (iii) one painted face?

  3. What number ending in 8 is doubled when the last digit is
     transferred to the beginning? [Hint: it may contain more
     digits than you expect.]