The following data gives the information on the observed lifetimes (in hours) of 225 electrical components:
Lifetimes (in hours) 0-20 20-40 40-60 60-80 80-100 100-120
Frequency 10 35 52 61 38 29
Determine the modal lifetimes of the components.

Here, the frequency of the class interval 60-80 is maximum. So, it is the modal class.

Now,
l = Lower limit of modal class = 60
f1 = Frequency of modal class = 61
f0 = Frequency of class preceding the modal class = 52
f2 = Frequency of class succeeding the modal class = 38
h = Class interval width = 20

So, Mode = l + ((f1 - f0) / (2f1 - f0 - f2)) * h
= 60 + ((61 - 52) / (2(61) - 52 - 38)) * 20
= 60 + (9 / (122 - 90)) * 20
= 60 + (9 / 32) * 20
= 60 + 5.625
Mode = 65.625

Therefore, the modal lifetime of electrical components is 65.625 hours