Question

Defects on plywood sheet occur at random with the average of one defect per 50 sq.ft. Find the probability that such a sheet has:

1. no defect
2. at least one defect
   Use e⁻¹ = 0.3678

Answer 1

Let X denote the number of defects on a plywood sheet.
Given, m = 1, e^–1 = 0.3678

∴ X ~ P(m) ≡ X ~ P(1)

The p.m.f. of X is given by

P(X = x) = `("e"^-"m" "m"^x)/(x!)`

∴ P(X = x) = `("e"^-1 (1)^x)/(x!)`

(i) P(no defects on a plywood)

= P(X = 0)

= `("e"^-1 (1)^0)/(0!)`

= `(0.3678 xx 1)/(1)`

= 0.3678

(ii) P(at least one defect)

= P(X ≥ 1)

= 1 – P(X = 0)

= 1 – 0.3678

= 0.6322