Answer:
3
Step-by-step explanation:
the question requires us to solve for the degree of freedom of this test.
we have this information below to answer this question
number on time = 90 95 85 60
sample size = 100 120 100 10
from this we can see that we have two rows, each row contains four piece of data, which gives us 4 columns
the formula for the degree of freedom:
df = (c-1)(r-1)
c = 4
r = 2
= 4-1 * 2-1
= 3 * 1
= 3
thank you!