How many restriction sites for EcoRI can be present in the DNA of $\mathrm{\lambda }$ bacteriophage?

The length of DNA of  $\mathrm{\lambda }$ bacteriophage is 48502 bp.

The length of restriction site for EcoR I is 6bp

The probability of occurrence of restriction site for EcoR I is $\frac{1}{4^6} = \frac{1}{4096}= \mathrm{Once} \mathrm{for} \mathrm{every} 4096 \mathrm{base} \mathrm{pairs}$.

No of restriction sites in the DNA of the phage is $\frac{48502}{4096}=11.8 =11 \mathrm{or} 12$