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The worm climbs 2 cm and falls 1 cm in 5 minutes.
So it effectively climbs (2-1)=1cm in 5 minutes.

For the first 8cm, it will take (8×5) = 40minutes

At the end of 40 minutes, it will be at 8 cm.

Then in another 5 minutes it will reach the top. Once it reaches the top, it won't fall again.
So the total time is 40+5=45 minutes
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Solution :
       length of pillar = 10 cm
   Effective distance climbed by worm in 5 mins = 2 cm - 1cm
       So it takes 5 minutes to climb 1 cm .
    Therefore time taken to climb 8cm = 8*5
Now the worm will climb 2cm  to reach 10cm , it wil take him 5 more minutes .

Therefore , total time taken to climb 10cm = 40 +5
                                                             =45 minutes!!

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