Evaluate
\frac{39b}{20}+\frac{639}{640}
Factor
\frac{3\left(416b+213\right)}{640}
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\frac{32\times 39b}{640}+\frac{639}{640}
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of 20 and 640 is 640. Multiply \frac{39b}{20} times \frac{32}{32}.
\frac{32\times 39b+639}{640}
Since \frac{32\times 39b}{640} and \frac{639}{640} have the same denominator, add them by adding their numerators.
\frac{1248b+639}{640}
Do the multiplications in 32\times 39b+639.
\frac{3\left(416b+213\right)}{640}
Factor out \frac{3}{640}.
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