Emily is training for a 10K race. On day one, she runs for 20 minutes. On day two, she runs for 30 minutes. On day three, she runs for 40 minutes. If this pattern continues, how many minutes will she run on day 8?

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