Discussion

The sum of three binary numbers 10110.10, 11010.01 and 10101.11 in decimal system is :

Answer: C

The sum is 70.50.

Convert each number, remembering that the first two places after the binary point are worth 1/2 and 1/4:

\[ \begin{aligned} 10110.10 &= 22.50 \\ 11010.01 &= 26.25 \\ 10101.11 &= 21.75 \\ \text{sum} &= 70.50 \end{aligned} \]

70.75 and 70.25 come from misreading one fractional part, and 69.50 from dropping a carry.

A useful check is that each binary fraction place halves in value: .1 is 0.5, .01 is 0.25 and .11 is 0.75.

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