Question 935441
B and C work an (approximately) equal number of days, and each works HALF the number of days that A works.


Let t be number of days that A worked, and the whole job to be done is 1.
The rule is RT=J for rate, time, job.  The rate expression is a little more complicated, since it is composed of a sum of terms.


I might be misunderstanding the description, but:
{{{(1/2)(1/10+1/30)t+(1/2)(1/10+1/60)t=1}}}
which shows half the days A and B do the work, and the other half of the days, A and C do the work, until the whole job is done.


Another understanding may be that half the days, A works alone and on the other half of the days, both B and C help:
{{{(1/2)(1/10)t+(1/2)(1/10+1/30+1/60)t=1}}}



One or the other of those should be the correct interpretation.  Solve for t  (and accept the result which seems to work right, or the one that matches your answer key if it's available).