Elitmus
Exam
Numerical Ability
Sequence and Series
1,3,6,10,15,21,28........................so on up to 300 terms then find the sum
Read Solution (Total 9)
-
- 1 ,3, 6, 10 is of the form n*(n+1)/2
n = 300
nth term = 300*(301)/2 = 45150
Then sum of these terms 1+3+6+10+15+......45150 ll be
Sum of n*(n+1)/2 terms
Sum of n*(n+1)/2 terms = 1/2* sum of [n^2 + n] terms
Sum of n^2 terms => n(n+1)(2n+1)/6
sum of n terms => n(n+1)/2
So Sum ll be 1/2 * [n(n+1)(2n+1)/6 + n(n+1)/2]
n(n+1)(2n+4)/12
n = 300
So 300(301)(604)/12 = 4545100
Ans : 4545100
- 10 years agoHelpfull: Yes(38) No(0)
- each term in the series follows the equation-n(n+1)/2, where n is the position
therefore for the sum of 300 terms of the series , we will apply summation over n(n+1)/2,
hence it will expand to-- ((n(n+1)(2n+1))/6)+(n(n+1)/2)
which will compute to 300*301*604/12
=4545100 - 10 years agoHelpfull: Yes(8) No(1)
- ans==4545100
- 10 years agoHelpfull: Yes(3) No(3)
- sn=n(a+l)/2.....
n=300,a=1,l=300
sn=300(301)/2
ans=45150 - 10 years agoHelpfull: Yes(3) No(4)
- =1+3+6+10+15+21+28+36+.............................up to 300 terms
=4+16+36+64+..................................up to 150 terms
=2^2+4^2+6^2+8^2+...........................up to 150 terms
=2^2*(1^2+2^2+3^2+4^2...........................up to 150 terms)
=4*(n*(n+1)*(2*n+1)/6)
put n=150
=2*(150*151*301)/3
=4545100
- 9 years agoHelpfull: Yes(3) No(0)
- n=300 and a=1 and d=1 so now we no the formula of ap series n/2[2a+(n-1)d]
300/2[2*1+(300-1)*1]
45150 - 10 years agoHelpfull: Yes(0) No(5)
- can someone tell me wat will be d diagram..i am got getting the question properly
- 10 years agoHelpfull: Yes(0) No(0)
- n=300,a=1,d=1,(the diffrence between successive terms in A.P..1,3-1,6-3,10-6,15-15....) we know the formula.sum of the nth terms in A.P=n/2(a+l)
=300/2(1+300)=45,150 - 10 years agoHelpfull: Yes(0) No(2)
- term are in the of n*(n+1)/2
sum of n^2 is n*(n+1)*(2*n+1)/12
sum of n term is n*(n+1)/2
so, sn=(n*(n+1)*(2*n+1)/12+n*(n+1)/2)/2
so ans 4545100
- 9 years agoHelpfull: Yes(0) No(0)
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