If \[{{x}_{1}},{{x}_{2}},.....{{x}_{20}}\]are in H.P. and \[{{x}_{1}},2,{{x}_{20}}\]are in G.P., then \[\sum\limits_{r=1}^{19}{{{x}_{r}}{{x}_{r+1}}}\]=

If \[{{x}_{1}},{{x}_{2}},.....{{x}_{20}}\]are in H.P. and \[{{x}_{1}},

1.	If \[{{x}_{1}},{{x}_{2}},.....{{x}_{20}}\]are in H.P. and \[{{x}_{1}},2,{{x}_{20}}\]are in G.P., then \[\sum\limits_{r=1}^{19}{{{x}_{r}}{{x}_{r+1}}}\]=
A.	76
B.	80
C.	84
D.	none of these
Answer» B. 80

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If \[{{x}_{1}},{{x}_{2}},.....{{x}_{20}}\]are in H.P. and \[{{x}_{1}},2,{{x}_{20}}\]are in G.P., then \[\sum\limits_{r=1}^{19}{{{x}_{r}}{{x}_{r+1}}}\]=

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