LIC AAO Model Paper 6

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Question : 59 of 160

Marks: +1, -0

If x =

1/2+1/6+1/{12}+1/{20}

+

1/{30} + 1/{42}+1/{56}+1/{63}

, then value of

1/x

is closest to

1.1
1
0.9
0.8
None of these

Solution:

x =

1/{1×2}+1/{2×3}+1/{3×4}

+ ..... +

1/{7×8} + 1/{7×9}

= 1 -

1/2+1/2-1/3+1/3-1/4

+ ..... +

1/6-1/7

+

1/7-1/8+1/{7×9}

= 1 -

1/8+1/{63}

=

{504-63+8}/{8×63}

=

{449}/{504}

∴

1/x

=

{504}/{449}

= 11

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