Chapter 4 - Number Representation and Calculation - 4.3 Computation in Positional Systems - Exercise Set 4.3 - Page 234: 27

$11_{two}$

$(1\times 1)_{10}=(1)_{10}=(1)_{2}$ Record the 1; there is nothing to carry. $\begin{array}{llll} & 1 & 1_{two} & \\ \times & & 1_{two} & \\ -- & -- & -- & \\ & & 1_{two} & \end{array}$ $(1\times 1)_{10}=(1)_{10}=(1)_{2}$ Result: $11_{two}$