Please tell answer with method please do fast

Answers (1)
S safeer

distance covered is the same

aversge\ speed=\frac{total\ distance}{total\ time}

Let d+d = 2d be the total distance

Let t1+t2 be the total time, then, 

v_{avg}=\frac{2d}{t_1+t_2}=\frac{2d}{\frac{d}{v_1}+\frac{d}{v_2}}=\frac{2v_1v_2}{v_1+v_2}

v_{avg}=\frac{2\times30\times20}{30+20}=\frac{1200}{50}=24m/s

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