In a family, there are three children, named Monu, Nonu and Sonu. One of them is 8 years old, the second one is 10 years old and the third one is 12 years old. Two statements from each child are collected and it is found that both the statements given by the 8-year-old child are true and both the statements given by the 10-year-old child are false. Whereas, out of the two statements given by the 12-year-old child, the first one is true and the second is false.

Following are the statements given by all the three children
Monu: Sonu is 12 years old, and I am 8 years old.
Sonu: Monu is 10 years old and Nonu is 12 years old.
Nonu: Sonu is 8 years old, and I am 10 years old .

Whatare the ages of Monu and Sonu, respectively?

Taking Monu to be the truth teller, 
Sonu is the 12 year old and Monu is the 8 year old. 
Sonu's first statement must be truth, but it says that Monu is 10 year old.
Therefore, this scenario is not possible. 

Taking Sonu to be the truth-teller.
This makes, Monu to be the 10 year old and nonu to be the 12 year old. 
Monu's both statement must be lies. 
Sonu is 8 year old, Monu is 10 year old. 
Nonu's first statement must be true and second msut be a lie, 
Sonu is 8 year old, Nonu is 12 year old. 

Taking Nonu to be the truth teller. 
This contradicts on the very first statement of Nonu, as he says that Sonu is the 8 year old. 
So Sonu must be the truth-teller. 

In all the case, the one in which Sonu was the truth-teller and 8 year old, satisfied all the conditions. 
Therefore, the ages of Monu and Sonu are, 10, 8 respectively.