[tex]\text {2 painters take} \longrightarrow 20 \text { hours}[/tex]
[tex]\text {1 painters will take} \longrightarrow 20 \times 2 = 40 \text { hours}[/tex]
P = number of painters.
[tex]\text {P painters will take} \longrightarrow 40 \div p = \dfrac{40}{p} \text { hours}[/tex]
t = total of times needed,
[tex]\boxed{\boxed {\text {Answer: }t = \dfrac{40}{p}}}[/tex]