Answer:
90 minutes
Step-by-step explanation:
Given that On day one, she runs for 20 minutes. On day two, she runs for 30 minutes. On day three, she runs for 40 minutes, this pattern may be presented as an arithmetic sequence shown below
20, 30, 40 ...
For an arithmetic sequence whose first term is a, and a common difference d, the nth term of the sequence may be given as
Tn = a + (n - 1)d
Hence the first term is 20, the common difference d is 10
On the 8th day, the 8th term
T8 = 20 + (8 - 1) 10
= 20 + 70
= 90 minutes
