Answer:
1 : 400,000
Explanation:
A map scale is usually represented as a unit fraction, one with 1 in the numerator. It has no units, which is to say that it is the ratio of same units.
It can be found by dividing the map dimension by the ground dimension when both are expressed in the same units.
(8.4 cm) / (33.6 km) = (8.4×10^-2 m) / (33.6×10^3 m) = (8.4/33.6)×10^-5
= 0.25×10^-5 = 1/400,000
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Additional comment
Map scales are often expressed using the colon for the ratio unit separator:
1 : 400,000