Answer : 1. "541 times"
Explanation :

Answer: A) 541 times Explanation: There are 60 minutes in an hour. In ¾ of an hour there are (60 × ¾) minutes = 45 minutes. In ¾ of an hour there are (60 × 45) seconds = 2700 seconds. Siren sounds for every 5 seconds. In 2700 seconds = 2700/5 = 540 times. The count start after the first sound, the Siren will sound 541 times in ¾ of an hour.