Discussion
If \(2.7 \times 10^{-6}\) is added to \(4.3 \times 10^{-5}\), giving due regard to significant figures, the result will be
Answer: B
The result is \(4.6 \times 10^{-5}\).
Write both numbers with the same power of ten and add:
\[ \begin{aligned} &0.27 \times 10^{-5} + 4.3 \times 10^{-5} \\ &= 4.57 \times 10^{-5} \end{aligned} \]
In addition, the result keeps only as many decimal places as the least precise term. In units of \(10^{-5}\), 4.3 is known to one decimal place, so the sum is rounded to one decimal place: \(4.6 \times 10^{-5}\).
\(4.57 \times 10^{-5}\) is the unrounded sum, \(4.5 \times 10^{-5}\) truncates instead of rounding, \(7.0 \times 10^{-5}\) adds the mantissas without matching the powers, and \(4.57 \times 10^{-6}\) has the wrong power.
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