11Are u sure qsn 2 is correct?
Coz the ans comes out to be 37.....
consider these sequences....112+(a-1).21 and 119+(b-1).21......a and b can take values 19 and 18 respy.....
Ques1) The first term of an A.P of conseutive integers is P2 +1. Show that the sum of (2P+1) terms of this series can be expressed as { P3 + (P+1) 3 } .
Ques2) Show that the number of numbers lying between 100 and 500 are divisible by 7 but not by 21 is 19.
Ques3) Show that the sum of 0.2 + 0.04 + 0.00006 + 0.0000008 + .......+ to infinity is (2000/9801).
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5 Answers
24sol1
a=P2+1
d=1 (becoz consecutive integers)
l=P2+2P+1
Now u can get the answer..[1]
11113rd one is an arithmetico geometric series....Use the std rules.....these are too easy friend...
1Q.2) 105 + (n-1)7 = 497
the no.of terms divisible by 7 = 57
105 + (n-1) 21 = 483
the no.of terms divisible by 21 = 19
thus, no. of terms divisible by 7 , but not by 21 = 57 - 19 = 38
