11/5

 8 x 400m with 2 min rest 

Round 1: 1:41.5
Round 2: 1:41.5
Round 3: 1:41.5 
Round 4: 1:40.7
Round 5: 1:43.8
Round 6: 1:43.6
Round 7: 1:46.4
Round 8: 1:46.7 

I guess maybe too hard at first? Much faster for first 4.