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Every seventh-grade student at Martin Middle School takes one world language class.
One-tenth of the seventh-grade students take French. Eighteen seventh-grade students take French.

Which equation represents s, the total number of seventh-grade students at the middle school?
18 = 0.1 s
18 = StartFraction 10 over s EndFraction
StartFraction s over 0.1 EndFraction = 18
10 s = 18