Answer: The battery was 19 percent full when the charging began.
Step-by-step explanation:
Since we have given that
Every minute, the percentage of the battery's capacity increased by = 2.5%
As we know that "Equation of line ":
[tex]y=mt+b\\\\Here, \\\\\text{ 't' represents number of minutes and 'b' represents initial battery }[/tex]
So, our equation becomes for now,
[tex]y=2.5t+b[/tex]
As we have given that,
After 17 minutes, the battery was 61.5% full.
So, our coordinate becomes (17,61.5)
So, it becomes
[tex]61.5=2.5\times 17+b\\\\61.5=42.5+b\\\\61.5-42.5=b\\\\19=b[/tex]
Hence, the battery was 19 percent full when the charging began.