A marathon is 26 miles.  He can run the first 10 miles in 1 hour.  For the remaining miles he runs at 80% that pace.  How long does the race take?
There are 26-10=<<26-10=16>>16 miles left for the rest of the race
He runs 10*.8=<<10*.8=8>>8 miles per hour
So it takes him 16/8=<<16/8=2>>2 hours
So in total it takes 1+2=<<1+2=3>>3 hours
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