Question

Mangala started doing physical exercise 10 minutes for the first day. She will increase the time of exercise by 5 minutes per day, till she reaches 45 minutes per days. How many days are required to reach 45 minutes?

• A. 7
• B. 8
• C. 9
• D. 4

Answer 1

The correct option is B 8

Mangala doing exercise first day $=10$ minutes. She will increase the time per day 5 minutes .so she doing exercise in two days $=15$ minutes. She doing exercise in three days $=20$ minutes
It means this becomes AP with first term $a=10$ and common difference $d=5$ and hence given last term $l=45$.
$\Rightarrow 10,15,\mathrm{20......},45$
Since $l=a+(n-1)d$
$\Rightarrow 45=10+(n-1)\times 5$
$\Rightarrow n-1=7$
$\Rightarrow n=8$