Question 535304
Shared work problems like this one can be solved by considering the faction of the work that can be done in some period of time by each resource and then summing them to a total of 1.
.
The older machine takes 104 minutes to do the work, so we can say it does 1/104 of the job per minute.  Working with the new machine, the job can be done in 40 minutes.
.
{{{ ( (1/104) + (1/x) ) *40 = 1 }}}
.
{{{ ( (x+104) / 104x )*40 = 1 }}}
.
{{{ 40*(x + 104) = 104*x }}}
.
{{{ 40x + 4160 = 104*x}}}
.
{{{ 4160 = 64*x}}}
.
{{{ 64*x = 4160}}}
.
{{{ x = 65}}}
.
So, the new machine can do the job in 65 minutes.
.
To check the work, compute how much work each machine will do in 40 minutes.
.
{{{ 40*(1/104) = 40/104 = .3846}}}
.
{{{ 40*(1/65) = 40/65 = .6154}}}
.
Correct.
.
Done.