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This problem trains for: SAT-I, GMAT, Math Kangaroo 5-6.

When the level of glucose in Dr. Charles Best's blood increased by 4% to 156 mg, he redoubled his efforts to discover insulin. What was his level of glucose before the increase?

Dr. Charles Best was one of the co-discoverers of insulin.

The level of 155 is the final amount. We have to find the initial amount x.

It is the initial amount that increased by 4% to result in 156 mg:

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His previous level of glucose was 150 mg (upper limit of the normal range).