The value of 1 - 1 + 1 - 1 + .........correct to 5 places

The value of
1 - 1 + 1 - 1 + .........correct to 5 places of decimal is :
20 20² 20³

Let S = 1 -	1	+	1	-	1	+ ........
	20		20²		20³

It is a geometric series to infinity with first term, a = 1

and common ratio ( r ) = -	1
	20

∴ S_∞ =	a
	1 - r

S_∞ =	20	= 0.9523809
	21

∴ The value correct to 5 places of decimal = 0.95238

1 -	1	+	1	-	1	+ .........correct to 5 places of decimal is :
	20		20²		20³