Latest Infosys Aptitude Question SOLUTION: 1, 7, 8,14,15,21,22,28,29 find sum of first 25 terms

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(#M40024452) INFOSYS Numerical Ability question Keep an EYE

1, 7, 8,14,15,21,22,28,29 find sum of first 25 terms

Asked In Infosys asxa asxaxax (10 years ago)

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varaprasad  (10 years ago)

dividing the given problem into 2 parts,
(1+8+15+22+...)+(7+14+21+28+...)
so, 13terms + 12terms
by using Arithmetic Progression
for (1+8+15+22+...)
a=1,d=7,n=13 and Sn=(2*a+(n-1)*d)*n/2
S13=(2*1+(13-1)*7)*13/2 = 559 ----(1)
for (7+14+21+28+...)
a=7, d=7, n=12
S12=(2*7+(12-1)*7)*12/2 = 546 ----(2)
so, eqn(1) + eqn(2) = 559 + 546 = 1105

ans:- 1105

Is this solution Helpfull? Yes (12) | No   

varaprasad  (10 years ago)

dividing the given problem into 2 parts,
(1+8+15+22+...)+(7+14+21+28+...)
so, 13terms + 12terms
by using Arithmetic Progression
for (1+8+15+22+...)
a=1,d=6,n=13 and Sn=(2*a+(n-1)*d)*n/2
S13=(2*1+(13-1)*6)*13/2 = 481 ----(1)
for (7+14+21+28+...)
a=7, d=7, n=12
S12=(2*7+(12-1)*7)*12/2 = 546 ----(2)
so, eqn(1) + eqn(2) = 481 + 546 = 1027

ans:- 1027

Is this solution Helpfull? Yes | No (9)  

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