# Average speed

The truck drove 1/2 of the way on the highway at 80km/h. The other half of the way 20km/h. Calculate the average speed

Result

v =  32 km/h

#### Solution:

$v_{ 1 } = 80 \ km/h \ \\ v_{ 2 } = 20 \ km/h \ \\ \ \\ v = s/t = s / (s/2/v_{ 1 } + s/2/v_{ 2 }) \ \\ v = 2 / (1/v_{ 1 } + 1/v_{ 2 }) = 2 / (1/80 + 1/20) = 32 = 32 \ \text { km/h }$

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