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If 11 A.M .'s are inserted between 28 and 10, then number of integral A.M 's is-

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Important Questions on Progression and Series

EASY
In an arithmetic progression, if the k th term is 5k+1 , then the sum of first 100 terms is
HARD
For any three positive real numbers a, b and c. If 925a2+b2+25c2-3ac=15b3a+c. Then
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Let a, b, c, d, e be natural numbers in an arithmetic progression such that a+b+c+d+e is the cube of an integer and b+c+d is a square of an integer. The least possible value of the number of digits of c is
HARD
The number of terms in an A.P. is even, the sum of the odd terms in it is 24 and that the even terms is 30. If the last term exceeds the first term by 1012, then the number of terms in the A.P. is 
MEDIUM
The sum of all two digit positive numbers which when divided by 7 yield 2 or 5 as remainder is
MEDIUM
If a1/x=b1/y=c1/z and a,b,c are in geometrical progression, then x,y,z are in
HARD
The houses on one side of a road are numbered using consecutive even numbers. The sum of the numbers of all the houses in that row is 170. If there are at least 6 houses in that row and a is the number of the sixth house, then
MEDIUM
The number of terms common to the two A.P.’s 3,7,11,,407 and 2,9,16,,709 is ____________.
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Let the sum of the first three terms of an A.P. be 39 and the sum of its last four terms be 178. If the first term of this A.P. is 10, then the median of the A.P. is :
MEDIUM
Three positive numbers form an increasing G.P. If the middle term in this G.P. is doubled, the new numbers are in A.P. Then the common ratio of the G.P. is :
HARD
Given an A.P. whose terms are all positive integers. The sum of its first nine terms is greater than 200 and less than 220.  If the second term in it is 12, then its 4th term is :
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Let X be the set consisting of the first 2018 terms of the arithmetic progression 1,6,11, , and Y be the set consisting of the first 2018 terms of the arithmetic progression 9,16,23,  . Then, the number of elements in the set XY is___.
MEDIUM
Let a1, a2, a3,,a49 be in A.P. such that Σ k = 0 1 2 a4k+1=416 and a9+a43=66. If a12+a22++a172=140m, then m is equal to:
MEDIUM
If the sum of the first n terms of the series 3+ 75+ 243+ 507+ is 4353, then n equals:
MEDIUM
Let a1, a2, a3,an, ,be in A.P. If a3+a7+a11+a15=72, then the sum of its first 17 terms is equal to :
HARD
Let AP a;d denote the set of all the terms of an infinite arithmetic progression with first term a and common difference d>0. If AP1;3AP2;5AP3;7=APa;d then a+d equals ____
MEDIUM
Let the sum of the first n terms of a non-constant A.P., a1, a2, a3, ...., an be 50n+n(n-7)2A, where A is a constant. If d is the common difference of this A.P., then the ordered pair d, a50 is equal to
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Let 1x1, 1x2,,1xn(xi0 for i=1, 2,., n) be in A.P. such that x1=4 and x21=20 . If n is the least positive integer for which xn>50, then i=1n1xi is equal to
MEDIUM
If x, y, z are positive numbers in A.P. and tan-1xtan-1y and  tan-1z are also in A.P., then which of the following is correct.
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If nC4, nC5 and nC6 are in A.P., then n can be