Xavier and Will take 2 days to assemble a toy house. Will and Ivan take 4 days to build the same house while Xavier and Ivan take only 2 days. How many complete days would the three of them take to build the same toy house?
Let the house be 1 P.

Fraction of the house assembled by Xavier and Will per day
= ¹₂ P

Fraction of the house assembled by Ivan and Will per day
= ¹₄ P

Fraction of the house assembled by Xavier and Ivan per day
= ¹₂ P

Combined rate
= (¹₂ + ¹₄ + ¹₂) ÷ 2
= (²₄ + ¹₄ + ²₄) ÷ 2
= ⁵₄  ÷ 2
= ⁵₄  x ¹₂
= ⁵₈ P 

Number of days taken by the three of them to build the same toy house
= 1 ÷ ⁵₈
= 1 x ⁸₅
= 1.60

Since the number of days needed is 1.60 days, therefore the total number of complete days needed to build the toy house is 2.

Answer(s): 2 days