The speed of a sparrow is x km/h in still air. When the

wind is blowing at 1 km/h, the sparrow takes 5 hours to fly

12 kilometres to her nest and 12 kilometres back again.

She goes out directly into the wind and returns with the wind

behind her. Find her speed in still air.

x = 5m/s

Step-by-step explanation:

Distance flying out = 12 km (headwind)

Distance flying back = 12 km (tailwind)

total distance = 12 + 12 = 24 km

wind speed = 1km/h

speed going out (with headwind) = (x - 1) km/h

speed coming back (with tailwind) = (x + 1) km/h

Time taken to go out = distance going out / speed going out

= 12 / (x-1)

Time taken to come back = distance coming back / speed coming back

= 12 / (x+1)

total time = time taken to go out + time taken to come back

5 = [ 12 / (x-1) ] + [ 12 / (x-1) ]

expanding this, we will get

5x² - 24x - 5 = 0

solving quadratic equation, we will get

x = - 1/5 (impossible because speed cannot be negative)

or

x = 5 (answer)