A.P

Algebra Level 4

The sums of the two Arithmetic Progressions are in the following order:

7 n + 1 : 4 n + 27 7n + 1 : 4n + 27

Find the simplified ratio of the 11th terms in the form of a : b a:b . Type your answer as a × b a \times b .


The answer is 12.

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1 solution

Syed Baqir
Sep 20, 2015

Let the first term and the common difference be :

a 1 , d 1 a n d a 2 a n d d 2 r e s p e c t i v e l y a_{1},\ d_{1}\ and\ a_{2}\ and\ d_{2}\ respectively 2 a 1 + ( n 1 ) d 1 ) a 2 + ( n 1 ) d 2 = 7 n + 1 4 n + 27 \frac {2a_{1}+(n-1)d_{1} )} {a_{2} + (n-1) d_{2} } = \frac {7n +1} {4n + 27 }

W e a r e s u p p o s e d t o f i n d t h e a 1 + 10 d 2 a 2 + 10 d 2 We\ are\ supposed\ to\ find\ the \frac { a_{1} + 10d_{2} } { a_{2} + 10 d_{2} }

t h e r e f o r e s u b s t i t u t e n = 21 w e w i l l g e t : therefore\ substitute\ n = 21 \ we\ will\ get : \quad

2 a 1 + 20 d 1 2 a 2 + 20 d 2 \rightarrow \frac {2a_{1} + 20d_{1} } { 2a_{2} + 20d_{2} } T h e A n s w e r d r o p s s i m p l y t o : The\ Answer\ drops\ simply\ to: 148 111 = 4 3 = 4 3 = 12 \frac {148}{111} = \frac {4} {3} = \huge \boxed { \color{#3D99F6}{ 4*3=12} }

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