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Question

Probability of guessing correctly atleast 7 out of 10 answers in a "True" or "False" test is =___

A
1164
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B
1132
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C
1116
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D
2732
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Solution

The correct option is C 1164
Each question can be answered in 2 ways (True or False)
Total ways in which 10 questions can be answered
=210
No. of ways of guessing at least 7 questions out of 10
=7 questions correct +8 questions correct +9 questions correct +10 questions correct
=10C7(1)7+10C8(1)8+10C9(1)9+10C10(1)10
=120+45+10+1
=176
Required Probability =176210=11×16210 =1164

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