Answer is C
Let the amount the man invested from the sum of Rs.15860 in the name of 3 sons be x, y and z. As the Simple Interest received is same,
$\frac{x*2*5}{100}=\frac{x*3*5}{100}=\frac{x*4*5}{100}$ = k, so
$x:y:z=\frac{100k}{10}:\frac{100k}{15}:\frac{100k}{20}$
Divide by 100k, we will get
$x:y:z=\frac{1}{10}:\frac{1}{15}:\frac{1}{20}$