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a&b

by shibal » Fri May 01, 2009 11:13 am
for any number a and b, a & b = a + b -ab
if a & b = 0, which of the following cannot be a value of b?

a 2
b 1
c 0
d -1
e -3/2

OA: B
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by dmateer25 » Fri May 01, 2009 11:25 am
0 = a + b – ab

ab = a + b

Now just plug in.

a) 2
2a = a + 2
a= 2

This works


b)1

a = a + 1
0 = 1

Doesn’t work
This has to be the answer.

c) 0

0 = a + 0
a = 0

This Works

d) -1

-a = a – 1
-2a = -1
a = 1/2

This Works


e) -3/2

-3a/2 = a – 3/2
-3a = 2a – 3
-5a = -3
a = 3/5

This works
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by maihuna » Fri May 01, 2009 11:30 am
there is an easy way out: as a&b = 0
a + b -ab = 0
=>a(b-1) = b
=> a = b/(b-1)

If b = 1 a will be INFINITY so b cant be 1
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