Question 699176
I can solve it by formula, and you can put it into a table.
You have to add their rates of working to get their
rate of working together.
Scientist's rate:
( 1 dose ) / ( 4 hrs )
Igor's rate:
( 1 dose ) / ( 12 hrs ) 
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Let {{{ t }}} = the time in hrs for them to make 1 dose
working together.
{{{ 1/4 + 1/12 = 1/t }}}
Multiply both sides by {{{ 12t }}}
{{{ 3t + t  = 12 }}}
{{{ 4t = 12 }}}
{{{ t = 3 }}} 
Working together they can make 1 dose in 3 hrs