Question

How prime minister has been elected

Answer 1

Prime Minister is elected by the MPs of the party who has majority in Lok Sabha. Lok Sabha has 545 seats. To win majority a party must win 273 seats. The MP's of winning party officially choose their leader who is the head of govt called the Prime Minister.
 
A prime minister must:

be a citizen of India.

be a member of the Lok Sabha or the Rajya Sabha. If the person chosen as the prime minister is neither a member of the Lok Sabha nor the Rajya Sabha at the time of selection, they must become a member of either of the houses within six months.

be above 25 years of age if they are a member of the Lok Sabha, or, above 30 years of age if they are a member of the Rajya Sabha.

not hold any office of profit under the Government of India or the government of any state or under any local or other authority subject to the control of any of the said governments.


Hope this helps..