7 1-57.  Subtract:   01111₂ - 10000₂ 1. 11111₂ negative 2. 00001₂ negative 3. 01111₂ positive 4. 10000₂ positive 1-58.  What is the radix of the octal number system? 1. 10₁₀ 2.       0 to 7 3.       8 4.       7₈ 1-59.  Which of the following is NOT a valid octal number? 1. 604₈ 2. 591₈ 3. 743₈ 4. 477₈ 1-60.  Which of the following equations is correct? 1. 8⁰ = 8 2. 8¹ = 1 3. 8⁴ = 8 8 8 4. 8² = 8 8 1-61.  One octal digit is represented by how many binary digits? 1.     One 2.     Two 3.     Three 4.     Four 1-62.  What is the decimal value of 8³? 1.       64₁₀ 2. 128₁₀ 3. 256₁₀ 4. 512₁₀ 1-63.  Which of the following symbols is the least significant digit of the octal number 1622.374? 1. 1 2. 2 3. 6 4. 4 1-64.  What is the sum of 4₈ and 4₈? 1. 10₁₀ 2. 10₈ 3.       7₈ 4. 16₈ 1-65.  What is the sum of 77₈ and 3₈? 1. 127₈ 2.       80₈ 3. 100₈ 4. 102₈ IN ANSWERING QUESTION 1-66, PERFORM THE INDICATED OPERATION. 1-66.  Add:     374₈ +  165₈ 1. 465₈ 2. 561₈ 3. 437₈ 4. 531₈ 1-67.  Find the sum of 7741₈ and 67₈. 1. 10000₈ 2. 10030₈ 3.       7030₈ 4. 10730₈ 1-68.  What is the sum of 7₈, 6₈, 5₈, and 4₈? 1. 22₈ 2. 17₈ 3. 26₈ 4. 24₈