Six years ago, the average of ages of Ravi, Mohan and Govind was 32 years.  If Shyam joins them now, the average of the ages of all four of them is 36 years.  The present age of Shyam is?

30

Six years ago average of Ravi, Mohan and Govind = 32 years

Present average of Ravi, Mohan and Govind = 32 + 6 = 38 years

Total present age of Ravi, Mohan and Govind = 38 × 3 = 114 years

Total present age of Ravi, Mohan, Govind and Shyam = 36 × 4 = 144 years

Hence,

Age of Shyam = 144 - 144 = 30 years