Correct Answer: 2/3 hrs
Explanation:
Let the original speed and time is S and T
 then distance = S x T
 Now the speed changes to 2/3S and T is T+20
 As the distance is same
 S x T = 2/3Sx(T+20)
 solving this we get t = 40 minutes 
 =40/60 = 2/3 hour
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