Abraham and Benedict builds a toy car in 8 hours.
Benedict and Chris builds a toy car in 4 hours.
Chris and Abraham builds a toy car in 7 hours.
How long does it take for Abraham, Benedict and Chris to build a toy car together?
Fraction of the toy car built by Abraham and Benedict in 1 hour = ¹₈ 
Fraction of the toy car built by Benedict and Chris in 1 hour = ¹₄ 
Fraction of the toy car built by Chris and Abraham in 1 hour = ¹₇ 

Total fraction of the toy car built by Abraham and Benedict and Chris in 1 hour
= (¹₈ + ¹₄ + ¹₇) ÷ 2
= (⁷₅₆ + ¹⁴₅₆ + ⁸₅₆) ÷ 2
= ²⁹₅₆ ÷ 2
= ²⁹₅₆ x ¹₂
= ²⁹₁₁₂ 

Time taken for Abraham, Benedict and Chris to build a toy car together
= 1 ÷ ²⁹₁₁₂
= 1 x ¹¹²₂₉
= 3²⁵₂₉ h

Answer(s): 3²⁵₂₉ h or 3²⁵₂₉ hours