Question

A video editor takes 15 hours to add a

Answer 1

So the Level III editor does it in 15 hours, the Level II(slower) does it in 25 hours and the Level I(even slower), does it in 34 hours.

now, since the Level III one does it in 15 hours, in 1 hour alone, how much has it done?  well, it only has done 1/15 of the whole work.

the Level II has 1 hour done only 1/25 of the whole work then, and the Level I has only done 1/34 of the whole work.

now, say they all do it in "t" hours, so how much have they edited in 1 hour altogether then?  well, they have only done 1/t.

$\bf \stackrel{\textit{Level III rate}}{\cfrac{1}{15}}+\stackrel{\textit{Level II rate}}{\cfrac{1}{25}}+\stackrel{\textit{Level I rate}}{\cfrac{1}{34}}~~=~~\stackrel{\textit{total work done}}{\cfrac{1}{t}} \\\\\\ \textit{doing a quick prime factoring, we end up with an LCD of }\underline{2550}~thus$

$\bf \cfrac{1}{15}+\cfrac{1}{25}+\cfrac{1}{34}=\cfrac{1}{t}\implies \cfrac{170~+~102~+~75}{2550}=\cfrac{1}{t}\implies \cfrac{247}{2550}=\cfrac{1}{t} \\\\\\ 247t=2550\implies t=\cfrac{2550}{247}\implies t=10\frac{80}{247}\implies t\approx 10hrs,~19min$