Question 910668
Very generally, two agents performing at rates 1/t and 1/T, so that the rate 1/T is for the small or slower, and 1/t is the rate for the faster bigger agent, then the combined rate for both agents working simultaneously on the same item will be the sum of their rates:


{{{(1/t+1/T)}}}
{{{(1/t)(T/T)+(1/T)(t/t)}}}
{{{T/(tT)+t/(tT)}}}
{{{highlight((T+t)/(tT))}}}


I have used lower case, t, for the shorter amount of time and upper case T for the bigger amount of time; the slower the agent, the larger the time for it to do the 1 unit of the job.