Let the total number of chocolates be x..
Santosh gave 1/4 of x to pinku = x/4.
Also, Santosh gave 1/3 of x to Poonam = x/3
Then x/3 + x/4 = 7x/12
Remaining.. = x-7x/12 = 5x/12
Santosh gave 50 chocolates to Alpana
Therefore,
5x/12=50
Or x=50*12/5=120
Therefore, total number of chocolates =120
Regards