Word problem help

Question

Cannot figure out the formula to this question? The wording does not make sense to me as to how I put it into a actual problem to solve?

 

Your 2010 fax machine can fax a large report in 9 minutes, while your 2014 fax machine can fax the same report in 8 minutes. How long would it take the two machines, working together, to fax the report? (Assume you have at least two machines for incoming faxes)

Answer 1

If the 2 machines are working in parallel, the reciprocals of the individual times add up to the reciprocal of the net time, making the net time smaller than ether individual time.

 

T₁ = time it takes 2010 machine to FAX = 9 min

T₂ = time it takes 2014 machine to FAX = 8 min

T = time it takes to FAX when they work together

 

1/T = 1/T₁ + 1/T₂ 

 

T = T₁T₂ / (T₁ + T₂) = [(9)(8) / (9 + 8)] min ≅ 4.235 min