Multiplying numbers in scientific notation Compute (12.6 × 10^6) * (10.5 × 10^3) and express the result in proper scientific notation (mantissa between 1 and 10).

Difficulty: Easy

Correct Answer: 1.32 × 10^11

Explanation:


Introduction / Context:
Scientific notation accelerates multiplication and division by separating magnitude (10^n) from the significant digits (mantissa). This is particularly helpful in electronics when combining values across very different scales, such as gains, frequencies, or time constants.


Given Data / Assumptions:

  • Numbers: 12.6 × 10^6 and 10.5 × 10^3.
  • We seek normalized scientific notation (1 ≤ mantissa < 10).
  • Arithmetic is exact to at least three significant digits.


Concept / Approach:
Multiply mantissas and add exponents: (a × 10^m) * (b × 10^n) = (a*b) × 10^(m+n). If the mantissa product is not between 1 and 10, re-normalize by adjusting the exponent accordingly. Keep an appropriate number of significant figures based on inputs (three sig figs here are reasonable: 12.6 and 10.5 each have three).


Step-by-Step Solution:

Multiply mantissas: 12.6 * 10.5 = 132.3.Add exponents: 10^6 * 10^3 = 10^(6+3) = 10^9.Combine: 132.3 × 10^9.Normalize mantissa: 132.3 × 10^9 = 1.323 × 10^11 (move decimal left two places, add 2 to exponent).


Verification / Alternative check:
Use a rounded mantissa to three significant digits consistent with inputs: 1.323 × 10^11 ≈ 1.32 × 10^11. A calculator check confirms the numeric value: 12.6e6 * 10.5e3 = 1.323e11, matching the normalized result.


Why Other Options Are Wrong:

13.2 × 10^11 and 13.2 × 10^12: mantissas are not normalized (should be between 1 and 10) and/or exponents are off by a power of ten.1.32 × 10^12: exponent too large by 10×.1.323 × 10^10: exponent too small by 10×.


Common Pitfalls:
Forgetting to renormalize the mantissa; adding exponents incorrectly; rounding too early, which can introduce noticeable errors when cascaded across multiple steps.


Final Answer:
1.32 × 10^11

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