Question

If $36$ workers can build a wall in $12$ days, how many days will $16$ workers take to build the same wall? (Assuming the number of working hours per day is constant)

Answer 1

If the number of workers decreases, the time to taken built the wall increases in the same proportion. Clearly, number of workers varies inversely to the number of days.
So here $\frac{x_1}{y_1}=\frac{x_2}{y_2}$ where
$x_1=36$ workers $y_1=12$ days
$x_2=16$ workers and $y_2=?$ days
Substitute, $\frac{36}{16}=\frac{y_2}{12}$ $\Rightarrow$ $y_2=\frac{12\times 36}{16}=27$ days
Therefore $16$ workers will build the same wall in $27$ days.