every 2 minutes, the monkey gains 2m (up 3, down 1).
That's 1m/min, so after 28min he's 28m up.
On min 29 he makes it to the top.
A monkey ascends a greased pole 30 m. high. He ascends 3 m. in Ist minute and descends 1m. in the next minute, again ascends 3m. in 3rd minute, but descends 1m. in 4th min and so on. In what time he reached the top?
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