Question 1168723
{{{1/3+1/y=1/2}}}


{{{1/y=1/2-1/3}}}

{{{6=3y-2y}}}

{{{highlight(6=y)}}}---------------Armando,  needs 6 hours if working alone.



Just to see more clearly:
Arman,  the father, work rate {{{1/3}}}
Armando, the son, work rate {{{1/y}}}
Both working together, work rate {{{1/2}}}
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Question asks what is the time needed for Armando, the son, the do 1 job by himself?


The rates are additive for working together, so {{{1/3+1/y=1/2}}}.