Answer:
Eight weeks
Step-by-step explanation:
Let's write the first few terms of your sequence.
20, 30, 40, 50, …
This is an arithmetic sequence, because there is a constant difference between consecutive terms.
The formula for an arithmetic sequence is
aₙ = a₁ + d(n -1 )
a₁ is the first term, and d is the difference in value between consecutive terms. Thus,
aₙ = 20 + 10(n-1)
You want to find the value of n when aₙ = 90 min.
90 = 20 + 10(n-1)
70 = 10(n-1)
7 = n - 1
n = 8
It will take you eight weeks until you are jogging for 90 min.
