In an alloy, the ratio of copper to zinc is $5:2$. If $1.250kg$ of zinc is mixed in $17.500kg$ of alloy, then what will be the new ratio of copper to zinc?

The correct option is C: $2:1$

Amount of copper $=\frac{5}{7}\times 17.5kg=12.5kg$

Amount of zinc $=17.5kg-12.5kg=5kg$.

When $1.250kg$ is mixed with the $17.500kg$ of alloy, then

Now, the amount of zinc in the above mixture $=(5+1.25)kg=6.25kg$

$\therefore$Required ratio of copper to zinc in the above mixture $=12.5:6.25$

$=\frac{12.5}{6.25}$

$=\frac{1250}{625}$

$=\frac{2}{1}=2:1$