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JAMB 1992 · UME · Q5

Simplify (1.25×104)×(2.0×10−1)6.25×105\dfrac{(1.25 \times 10^4) \times (2.0 \times 10^{-1})}{6.25 \times 10^5}.

Worked solution (try it first)
  1. Top: 1.25×2.0=2.51.25 \times 2.0 = 2.5 and 104×10−1=10310^4 \times 10^{-1} = 10^3, so the top is 2.5×1032.5 \times 10^3.
  2. Divide: 2.5÷6.25=0.42.5 \div 6.25 = 0.4 and 103÷105=10−210^3 \div 10^5 = 10^{-2}, giving 0.4×10−20.4 \times 10^{-2}.
  3. 0.4 is not between 1 and 10, so write it as 4×10−14 \times 10^{-1}.
  4. The value is 4.0×10−34.0 \times 10^{-3}, option A.

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