EASY
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IMPORTANT
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Let 3, 6, 9, 12,  upto 78 terms and 5, 9, 13, 17,  upto 59 terms be two series. Then, the sum of the terms common to both the series is equal to ______.

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Important Questions on Sequences and Series

HARD
JEE Main
IMPORTANT
Let a,b be two non-zero real numbers. If p and r are the roots of the equation x2-8ax+2a=0 and q and s are the roots of the equation x2+12bx+6b=0, such that 1p,1q,1r,1 s are in A.P., then a-1-b-1 is equal to _____ .
MEDIUM
JEE Main
IMPORTANT
Let a1=b1=1,an=an-1+2 and bn=an+bn-1 for every natural number n2. Then n=115an·bn is equal to _____ .
MEDIUM
JEE Main
IMPORTANT
Consider two G.Ps. 2,22,23, and 4,42,43, of 60 and n terms respectively. If the geometric mean of all the 60+n terms is 22258, then k=1nkn-k is equal to:
MEDIUM
JEE Main
IMPORTANT
The series of positive multiples of 3 is divided into sets : 3,6,9,12,15,18,21,24,27, Then the sum of the elements in the 11th  set is equal to _______.
MEDIUM
JEE Main
IMPORTANT
If k=110kk4+k2+1=mn, where m and n are co-prime, then m+n is equal to
MEDIUM
JEE Main
IMPORTANT
Different A.P.'s are constructed with the first term 100, the last term 199, And integral common differences. The sum of the common differences of all such, A.P's having at least 3 terms and at most 33 terms is.
MEDIUM
JEE Main
IMPORTANT
Suppose a1,a2,,an, be an arithmetic progression of natural numbers. If the ratio of the sum of the first five terms to the sum of first nine terms of the progression is 5:17 and 110<a15<120, then the sum of the first ten terms of the progression is equal to