Question

Answer 1/5d + 1/8d=2

Answer 1

$\frac{1}{5}d+\frac{1}{8}d=2\\\\ Make\ common\ denominator\ of\ \frac{1}{5}\ and\ \frac{1}{8}\ which\ is\ 40:\\\\ \frac{8}{40}d+\frac{5}{40}d=2\ \ \ |*40\\\\8d+5d=2*40\\\\ 13d=80\ \ |:13\\\\d=\frac{80}{13}=6\frac{2}{13}\\\\ Answer\ is\ d=6\frac{2}{13}.$

Answer 2

I thought you're saying that the denominators are 5d and 8d.

If so, then the common denominator is  40d, and 'd' turns out to be  13/80 .