The following data gives the information on the observed lifetimes (in hours) of 225
electrical components:

Lifetime (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.

From the given data the modal class is 60–80.

l = 60,

The frequencies are:

f_m = 61, f₁ = 52, f₂ = 38 and h = 20

The formula to find the mode is

Mode = l+ [$\frac{f_m-f_1}{2f_m-f_1-f_2}$]×h

Substitute the values in the formula, we get

Mode =60+[$\frac{61-52}{122-52-38}$]×20

Mode = 60+($\frac{9\times 20}{32}$)

Mode = 60+($\frac{45}{8}$) = 60+ 5.625

Therefore, modal lifetime of the components = 65.625 hours.