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A race course is 400 metres long. A and B run a race and A wins by 5 metres. B and C run over the same course and B wins by 4 metres. C and D run over it and D wins by 16 metres. If A and D run over it, then who would win and by how much?
A wins over B by 5 m :
$$\dfrac{\ V_A}{V_B}=\dfrac{\ 400}{395}=\dfrac{\ 80}{79}$$
B wins over C by 4 m :
$$\dfrac{\ V_B}{V_C}=\dfrac{\ 400}{396}=\dfrac{\ 100}{99}$$
D wins over C by 16 m :
$$\dfrac{\ V_D}{V_C}=\dfrac{\ 400}{384}=\dfrac{\ 25}{24}$$
$$\rightarrow$$ Hence, $$\left(\dfrac{\ V_A}{V_B}\right)\ \left(\dfrac{\ V_B}{V_C}\right)\ \left(\dfrac{\ V_C}{V_D}\right)=\ \dfrac{\ 80}{79}\times\dfrac{\ 100}{99}\times\dfrac{\ 24}{25}$$
$$=\ \dfrac{\ V_A}{V_D}=\ \dfrac{\ 80\times32}{79\times33}$$
$$=\dfrac{V_A}{V_D}=\ \dfrac{2560\ }{2607}=\ \dfrac{\ 400-x}{400}$$
Therefore, $$x=7.21\ m$$ .
Therefore, D wins over A by 7.21 metres.
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