Number of songs sung. There were 750 people when the first song was sung. After each song, 50 people are leaving the hall. How many songs are sung to make them zero? 
The answer is 16, I am unable to understand it. I am getting 15 as the answer. Please explain.

Listen to the question carefully: "There were $750$ people when the first song was sung"
First song was already sung  $+1$;
remaining people is $750$.
$750/50=15$;
Answer is $15+1=16$
