Infosys
Company
Numerical Ability
Arithmetic
1, 7, 8,14,15,21,22,28,29 find sum of first 25 terms
Read Solution (Total 2)
-
- 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 - 10 years agoHelpfull: Yes(12) No(0)
- 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 - 10 years agoHelpfull: Yes(0) No(9)
Infosys Other Question