Q: 6 (IAS/2005)

There are 10 identical coins and each one of them has ‘H’ engraved on its one face and “T” engraved on its other face. These 10 coins are lying on a table and each one of them has ‘H’ face as the upper face. In one attempt, exactly four (neither more nor less) coins can be turned upside down. What is the minimum total number of attempts in which the “T” faces of all the 10 coins can be brought to be the upper faces ?
question_subject: 
Maths
question_year: 
2005
question_exam: 
IAS
question_sub_subject: 
Mathematics
question_topic: 
Mathematics
stats: 
0,128,112,128,80,16,16