Question

On a 100 kilometre track A train travels the first 30 km at a uniform speed of 30 km per hour. how

much fast must the train travel the next 70 kilometre so as to average 40 kilometre per hour for the

entire trip?
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Answer 1

i think hopefully the answer is 50 km

Answer 2

avg velocity is total displacement divided total time taken

$40 = \frac{100}{30 \div 30 + 70 \div x}$

$1 + 70 \div x = \frac{100}{40}$

$\frac{70}{x} = 3 \div 2$

and after solving for x answer will be 46.6