Convert the mixed fraction into an improper fraction
An improper fraction is obtained by adding the whole part with a fractional Part of a mixed fraction.
Therefore,
312=3+12=3×2+12=6+12=72
Find the simplest form of given ratio
⇒312:7=72:71
=72÷71=72×17=12
⇒312:7=1:2
Hence, the simplest form of the ratio
312:7 is 1:2