2 hours and 50 minutes = 2.5/6 hours.

2 5/6(X+24)=3(X-24)

17/6X+68=3X-72

140= 1/6X

X=840

(840-24)×3=2448 km

A: When there is no wind, the speed of the plane is 840 km/h and the total range is 2448 km. References:

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Solution: Suppose it takes X hours to complete the rest of the second grade:

(2/ 15+ 1/5)+ 1/5 = x

x= 10/3

10/3+1=13/3 hours