Question 58898
Let Jo's speed be xmph
Total distance travelled by Jo = 12 miles.
So time taken by Jo = 12/x hrs

Speed of Chris for travelling from A to B = 2x mph
A to B = 4 miles
So time taken = 4/2x
              = 2/x hrs

Speed of Chris for travelling from B to C = x mph
B to C = 4 miles
So time taken = 4/x
              = 4/x hrs

Speed of Chris for travelling from C to A = x/2 mph
C to A = 4 miles
So time taken = 4/(x/2)
              = 8/x hrs

So total time taken = 2/x + 4/x + 8/x
                    = 14/x hrs

Comparing , we find that Jo reached A first as the time taken by her was only 12/x hrs

Distance covered by Chris in 12/x hrs = (12/x)/ (14/x) * 12
                                      = 10.3 miles

So Jo is ahead of Chris by 12 - 10.3 = 1.7 miles