If ${{\text{a}}_1},{{\text{a}}_2},{{\text{a}}_3},.............,{{\text{a}}_n}$ are in arithmetic progression and ${{\text{a}}_1}{\text{ + }}{{\text{a}}_4} + {{\text{a}}_7} + ............. + {{\text{a}}_{16}} = 114$, then ${{\text{a}}_1}{\text{ + }}{{\text{a}}_6} + {{\text{a}}_{11}} + {{\text{a}}_{16}}$ is equal to:
$
{\text{A}}{\text{. 38}} \\
{\text{B}}{\text{. 98}} \\
{\text{C}}{\text{. 76}} \\
{\text{D}}{\text{. 64}} \\
$
Answer
682.8k+ views
Hint – Use the property of A.P. In case of arithmetic progressions, the difference between two adjacent terms always remains constant throughout the entire progression.
Complete step by step answer:
Given Data,
${{\text{a}}_1}{\text{ + }}{{\text{a}}_4} + {{\text{a}}_7} + {{\text{a}}_{10}} + {{\text{a}}_{13}} + {{\text{a}}_{16}} = 114{\text{ - - - Equation 1}}$
Looking at the above series, we can make out that
${{\text{a}}_1}{\text{ + }}{{\text{a}}_{16}}{\text{ = }}{{\text{a}}_7} + {{\text{a}}_{10}}{\text{ = }}{{\text{a}}_{13}} + {{\text{a}}_4}$
On substituting, equation 1 now becomes
$
{\text{3}}\left( {{{\text{a}}_1}{\text{ + }}{{\text{a}}_{16}}} \right) = 114 \\
\Rightarrow {{\text{a}}_1}{\text{ + }}{{\text{a}}_{16}} = 38.{\text{ - - - Equation 2}} \\
$
We are supposed to find out the value of, ${{\text{a}}_1}{\text{ + }}{{\text{a}}_6} + {{\text{a}}_{11}} + {{\text{a}}_{16}}$
Here, we can observe ${{\text{a}}_1}{\text{ + }}{{\text{a}}_{16}}{\text{ = }}{{\text{a}}_{11}} + {{\text{a}}_6}$
$
\Rightarrow {{\text{a}}_1}{\text{ + }}{{\text{a}}_6} + {{\text{a}}_{11}} + {{\text{a}}_{16}} = 2\left( {{{\text{a}}_1}{\text{ + }}{{\text{a}}_{16}}} \right) \\
\Rightarrow {{\text{a}}_1}{\text{ + }}{{\text{a}}_6} + {{\text{a}}_{11}} + {{\text{a}}_{16}} = 2\left( {38} \right){\text{ (from equation 2)}} \\
\Rightarrow {{\text{a}}_1}{\text{ + }}{{\text{a}}_6} + {{\text{a}}_{11}} + {{\text{a}}_{16}} = 76. \\
\\
$
Hence Option C is the correct answer.
Note – In order to solve problems like this, always look out for similarities or repetitions in the given series. Make use of it to simplify the arithmetic progression, find out the value of a term or a set of terms, the rest can be found out by direct substitution.
Complete step by step answer:
Given Data,
${{\text{a}}_1}{\text{ + }}{{\text{a}}_4} + {{\text{a}}_7} + {{\text{a}}_{10}} + {{\text{a}}_{13}} + {{\text{a}}_{16}} = 114{\text{ - - - Equation 1}}$
Looking at the above series, we can make out that
${{\text{a}}_1}{\text{ + }}{{\text{a}}_{16}}{\text{ = }}{{\text{a}}_7} + {{\text{a}}_{10}}{\text{ = }}{{\text{a}}_{13}} + {{\text{a}}_4}$
On substituting, equation 1 now becomes
$
{\text{3}}\left( {{{\text{a}}_1}{\text{ + }}{{\text{a}}_{16}}} \right) = 114 \\
\Rightarrow {{\text{a}}_1}{\text{ + }}{{\text{a}}_{16}} = 38.{\text{ - - - Equation 2}} \\
$
We are supposed to find out the value of, ${{\text{a}}_1}{\text{ + }}{{\text{a}}_6} + {{\text{a}}_{11}} + {{\text{a}}_{16}}$
Here, we can observe ${{\text{a}}_1}{\text{ + }}{{\text{a}}_{16}}{\text{ = }}{{\text{a}}_{11}} + {{\text{a}}_6}$
$
\Rightarrow {{\text{a}}_1}{\text{ + }}{{\text{a}}_6} + {{\text{a}}_{11}} + {{\text{a}}_{16}} = 2\left( {{{\text{a}}_1}{\text{ + }}{{\text{a}}_{16}}} \right) \\
\Rightarrow {{\text{a}}_1}{\text{ + }}{{\text{a}}_6} + {{\text{a}}_{11}} + {{\text{a}}_{16}} = 2\left( {38} \right){\text{ (from equation 2)}} \\
\Rightarrow {{\text{a}}_1}{\text{ + }}{{\text{a}}_6} + {{\text{a}}_{11}} + {{\text{a}}_{16}} = 76. \\
\\
$
Hence Option C is the correct answer.
Note – In order to solve problems like this, always look out for similarities or repetitions in the given series. Make use of it to simplify the arithmetic progression, find out the value of a term or a set of terms, the rest can be found out by direct substitution.
Recently Updated Pages
A Paragraph on Pollution in about 100-150 Words

What is BLO What is the full form of BLO class 8 social science CBSE

10 examples of friction in our daily life

Draw a diagram of nephron and explain its structur class 11 biology CBSE

Write structures of the following compounds i 2 Chloro3methylpentane class 11 chemistry CBSE

XIX+XXX A 49 B 51 C 55 D 44 class 5 maths CBSE

Trending doubts
Explain the Treaty of Vienna of 1815 class 10 social science CBSE

1 GB equals how many MB?

10 examples of evaporation in daily life with explanations

What is the full form of POSCO class 10 social science CBSE

Which is the hottest planet in the Solar system A Earth class 10 social science CBSE

Name any four life processes in living things class 10 biology CBSE

