Chapter 6 - Section 6.3 - Permutations and Combinations - Exercises - Page 414: 35

45 strings

We have 8 zeros and 10 ones 0 must be immediately followed by 1 So we have eight $01$ and two $1$ to arrange. The arrangements for $n$ objects with $r$ similar objects is given by $\frac{n!}{r!}$ So in our case we have eight $01$ and two $1$ to arrange i.e total 10 objects. Hence it is given by $\frac{10!}{8!.2!}$ = 45