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# aqa A2 computing --- floating point watch

1. hey guys can any one tell and and go through step by step why the ans is -2.5 for question 3b ?

http://filestore.aqa.org.uk/subjects...W-QP-JUN11.PDF
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4. The first part of the question is the Mantissa, this one has eight bits and where the dot is, it kind of represents 0 on a number line. On the left of it you get the bit positions 1,2,4,8,16 and so on and on the right you get bits in the form of fractions in the order 1/2,1/4,1/8,1/16 and so on. The exponent here is a 4 bit exponent and gives the decimal number 2 and with this number you move the dot 2 places to the right. If the exponent was a negative exponent (started with a 1) you would move it X places to the left. Since you move the mantissa 2 places right it becomes 101.10000
The mantissa was negative since it starts with a 1, so when you add the bits up it is
-4+1+0.5 = -2.5

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