LCM of 24,36 and 48 is 144.
so let the work be of eating 144 chocolates.
A eats 6 chocolates per day, B eats 4 chocolates per day and C eats 3 chocolates per day.
Together they will eat 13 chocolates per day.
they worked for 4 days together so they ate=13 x4=52 chocolates
Number of chocolates left=144-52=92
A left 3 days before completion so B had to work alone, so he ate =3x4=12chocolates alone
number of chocolates left =92-12=80 chocolates
A and B eat 10 chocolates together so tehy took 8 days when they were together.
THus the work will be completed in=4+8+3=15 days.
