In a factory, machine A produces $30\%$ of total output, machine B produces $25\%$ and the machine $\mathit{C}$ produces the remaining output. The defective items produced by machines $\mathrm{A},\mathrm{B}$ and $\mathrm{C}$ are $1\%,1.2\%,2\%$ respectively. An item is picked at random from a day's output and found to be defective. Find the probability that it was produced by machine $\mathrm{B}$ ?