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| 1. |
Find Sum of : -\xa0 8 + 88 + 888 + 8888 +.............upto n number of terms. |
| Answer» Ans. Sn\xa0= 8( 1 + 11 + 111 + 1111 + ..... Upto n terms )=> 8/9 (9\xa0+ 99 + 999 + 9999 + ……… upto n terms)=> 8/9 [ (10-1) + (100-1) + (1000-1) + upto n terms]=> 8/9 [ (10 + 100 + 1000 + ...... n terms ) -(1+ 1 + 1 + ………… n terms)]=> 8/9 [ 10(10n\xa0-1)/ (10-1) - n ]=> 8/9 [ 10(10n-1)/9 - n]=> 80(10n\xa0-1) /81 - 8n/9 | |