Answer:
Option B.
Step-by-step explanation:
It is given that erza is training for a track race. He starts by sprinting 100 yards. he gradually increases his distance, adding 5 yards a day for 21 days. So, the required sequence is
100, 105, 110, 115, ...
It is an AP. Here,
First term = 100
Common difference = 5
Explicit formula for an AP is
[tex]a_n=a_1+(n-1)d[/tex]
where, [tex]a_1[/tex] is first term and d is common difference of the AP.
Substitute [tex]a_1=100\text{ and }d=5[/tex] in the above formula.
[tex]a_n=100+(n-1)5[/tex]
Therefore, the required explicit formula is [tex]a_n=100+(n-1)5[/tex].
Hence, option B is correct.