To find the class mark for each interval, the following relation is used.
xᵢ = (Upper limit + Lower limit)/2
Class size (h) of this data = 20.Taking 150 as assured mean (a), dᵢ, uᵢ, and fᵢuᵢ can be calculated as follows.

From the table, it can be observed that
∑fᵢ = 50, ∑fᵢuᵢ = 12, a = 150 and h = 20
mean(X̄) = a + (∑fᵢuᵢ/∑fᵢ)h = 150 + (-12/50) × 20 = 150 – 24/5 = 150 – 4.8 = 145.2
Therefore, the mean daily wage of the workers of the factory is ₹145.20