Flying against the jetstream a jet travels 3450km in 5 hours

Flying against the jetstream, a jet travels 3450km in 5 hours. Flying with the jetstream, the same jet travels 8400km in 8 hours. What is the speed of the jet in still air, and what is the speed of the jetstream?

Solution

j = speed of jetstream
a = speed of plane in still air
against jetstream:
-j + a = 3450/5
with jetstream
+j + a = 8400/8
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do divisions
-j + a = 690
+j + a = 1050
add the equations
2a = 1740
a = 870 km/hr speed of plane in still air
-j + 870 = 690
j = 870 - 690
j = 180 km/hr speed of jetstream
check in other equation
180 + 870 = 1050