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JAMB 1989 · UME · Q6

What is the difference between 0.007685 correct to three significant figures and 0.007685 correct to four decimal places?

Worked solution (try it first)
  1. To 3 significant figures: the zeros after the point don't count, so keep 7, 6, 8 and look at the 5.
  2. Round up: 0.00769.
  3. To 4 decimal places: keep 0.0076 and look at the fifth decimal, 8.
  4. Round up: 0.0077.
  5. The difference is 0.0077−0.00769=0.00001=10−50.0077 - 0.00769 = 0.00001 = 10^{-5}, option A.

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