(a) Convert the following numbers to be stated bases: (i) 125.625, to binary (ii) 111011.10011, to octal (b) Given that X = 11011011 and Y= 11101101, (i) co...

Assessment: WAEC SSCE - Computer Studies - 2016 (Essay) Subject: Computer Studies

Question 1 Report

(a) Convert the following numbers to be stated bases:

(i) 125.625, to binary

(ii) 111011.10011, to octal

(b) Given that X = 11011011 and Y= 11101101,

(i) construct the truth table for X, Y Z;

(ii) draw the logic gate of X, Y = Z

(iii) state the value of Z.

Answer Details

(a) Number-base conversions

(i) Convert \(125.625_{10}\) to base 2.

For the integer part, successive division by 2 gives:

DivisionQuotientRemainder
125 ÷ 2621
62 ÷ 2310
31 ÷ 2151
15 ÷ 271
7 ÷ 231
3 ÷ 211
1 ÷ 201

Reading the remainders from bottom to top gives \(125_{10}=1111101_2\).

For the fractional part:

\(0.625\times2=1.25\), giving 1;
\(0.25\times2=0.5\), giving 0;
\(0.5\times2=1.0\), giving 1.

Therefore, \(0.625_{10}=0.101_2\), and hence

\[\boxed{125.625_{10}=1111101.101_2}\]

(ii) Convert \(111011.10011_2\) to base 8. Group the binary digits in threes from the binary point:

\[111\;011.100\;110_2=73.46_8\]

\[\boxed{111011.10011_2=73.46_8}\]


(b) \(X=11011011\), \(Y=11101101\), and \(Z=X\mathbin{\text{ AND }}Y\).

(i) Truth table for the AND operation

XYZ = X AND Y
000
010
100
111

(ii) Logic-gate diagram

figure
Two-input AND logic gate, where \(Z=X\text{ AND }Y\).

(iii) Value of \(Z\)

Bit position12345678
X11011011
Y11101101
Z11001001

\[\boxed{Z=11001001_2}\]

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