Question 1022752
<pre>
Here is the way your teacher most probably wants you to
solve it:

The number of workers and the number of days required
are inversely proportional (one increases if the other
decreases), so we set up the proportions in reverse
order:

{{{matrix(1,5,Number,of,workers,FIRST,time)/matrix(1,5,Number,of,workers,SECOND,time)}}}{{{""=""}}}{{{matrix(1,5,Number,of,days,SECOND,time)/matrix(1,5,Number,of,days,FIRST,time)}}}

Let the number of days the SECOND time be N

{{{15/25}}}{{{""=""}}}{{{N/20}}}

Cross-multiply:

{{{25N}}}{{{""=""}}}{{{300}}}

Divide both sides by 25

{{{N}}}{{{""=""}}}{{{300/25}}}

{{{N}}}{{{""=""}}}{{{12}}}

So it will take 12 days.

Edwin</pre>