Proportion questions relating with 3 subjects .

Question

Eight men can build two houses in 20 days. How man men does it take to build 3 houses in 15 days

My workings :

$2 houses = 20 days$ $3 houses = 20.2.3= 120 days$

$1 men = 2 houses = 1/20 days$

$1 men = 3 houses = 1/120 days$

Answer 1

If $x$ is the time (in hours) required for one man to build a house, then $$ 8\frac{1}{x}=\frac{2}{20}\Leftrightarrow x=80 $$ Thus, if $n$ men are needed to build $3$ houses in $15$ days, we have: $$ n\frac{1}{80}=\frac{3}{15}\Leftrightarrow n=16 $$