CPM Homework Help : PC3 Problem 12-118

Given the infinite sum $a − \frac { a } { 2 } + \frac { a } { 4 } - \frac { a } { 8 }+\: ... = 24$ , what is the value of $a$ ?

Hint:

$S=\frac{a}{1-r}$

More Help:

$r=-\frac{1}{2}$

Step:

$24=\frac{a}{1-(1/2)}$