find the number of different possible A.P's of 5 terms from first 20 natural number....solve it guys
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Step-by-step explanation:
Total ways of selecting consecutive no.s are (1,2,3,4),(2,3,4,5),(3,4,5,6),........,(17,18,19,20)=17 possible ways
Total ways of selecting non consecutive no.s = Total ways of selecting - Total ways of selecting consecutive no.s
=
20
C
4
−17
=19×15×17−17
=17(19×15−1)=284×17
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