GMAT Critical Reasoning (CR) | The Earth's rivers constantly carry dissolved salts into its oceans.

Assume we know in hundred years salt level increases by 10 units and 1 unit is used by biological activity. So effectively salt level increases by 9 units every hundred years. So if we know increase in the salt level in the past hundred years ,we can find out how long it took to reach the current level from salt free level even if some salt is used by biological activity. The biological activity would have been there all along. E need not be assumed

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