Adrian and Benjamin builds a toy car in 2 hours.
Benjamin and Charlie builds a toy car in 9 hours.
Charlie and Adrian builds a toy car in 3 hours.
How long does it take for Adrian, Benjamin and Charlie to build a toy car together?
Fraction of the toy car built by Adrian and Benjamin in 1 hour = ¹₂ 
Fraction of the toy car built by Benjamin and Charlie in 1 hour = ¹₉ 
Fraction of the toy car built by Charlie and Adrian in 1 hour = ¹₃ 

Total fraction of the toy car built by Adrian and Benjamin and Charlie in 1 hour
= (¹₂ + ¹₉ + ¹₃) ÷ 2
= (⁹₁₈ + ²₁₈ + ⁶₁₈) ÷ 2
= ¹⁷₁₈ ÷ 2
= ¹⁷₁₈ x ¹₂
= ¹⁷₃₆ 

Time taken for Adrian, Benjamin and Charlie to build a toy car together
= 1 ÷ ¹⁷₃₆
= 1 x ³⁶₁₇
= 2²₁₇ h

Answer(s): 2²₁₇ h or 2²₁₇ hours