Adrian and Brendon builds a toy car in 5 hours.
Brendon and Charles builds a toy car in 10 hours.
Charles and Adrian builds a toy car in 3 hours.
How long does it take for Adrian, Brendon and Charles to build a toy car together?
Fraction of the toy car built by Adrian and Brendon in 1 hour = ¹₅ 
Fraction of the toy car built by Brendon and Charles in 1 hour = ¹₁₀ 
Fraction of the toy car built by Charles and Adrian in 1 hour = ¹₃ 

Total fraction of the toy car built by Adrian and Brendon and Charles in 1 hour
= (¹₅ + ¹₁₀ + ¹₃) ÷ 2
= (⁶₃₀ + ³₃₀ + ¹⁰₃₀) ÷ 2
= ¹⁹₃₀ ÷ 2
= ¹⁹₃₀ x ¹₂
= ¹⁹₆₀ 

Time taken for Adrian, Brendon and Charles to build a toy car together
= 1 ÷ ¹⁹₆₀
= 1 x ⁶⁰₁₉
= 3³₁₉ h

Answer(s): 3³₁₉ h or 3³₁₉ hours