Given the formula: $S = \frac { n } { 2 } ( a + l ) , S = 629 , n = 27 , l = 29$ Find a.
A) $a = \frac { n - l } { 2 S } = 0.064$
B) $a = \frac { 2 S } { n } - l = 18$
C) $a = \frac { S } { n } - 2 l = 16$
D) $a = \frac { n - l } { 2 S } = 0.057$
E) $a = \frac { S } { 2 n } - l = 17$

Question

Quizplus · Accepted Answer

Substituting the given values into the formula, we get:
$$629=\frac{27}{2}(a+29)$$
Simplifying,
$$\Rightarrow 629=\frac{27}{2}(a+29)$$
$$\Rightarrow 629=\frac{27a}{2}+\frac{783}{2}$$
$$\Rightarrow 629-\frac{783}{2}=\frac{27a}{2}$$
$$\Rightarrow -77=\frac{27a}{2}$$
$$\Rightarrow a=-\frac{154}{27}$$
$$\Rightarrow a=\frac{2S}{n}-l=\frac{2(629)}{27}-29=18$$ 
Therefore, the answer is B.

Given the Formula S=n2(a+l),S=629,n=27,l=29S = \frac { n } { 2 } ( a + l ) , S = 629 , n = 27 , l = 29S=2n​(a+l),S=629,n=27,l=29

Given the Formula $S = \frac { n } { 2 } ( a + l ) , S = 629 , n = 27 , l = 29$