The following 12 words on average account for a quarter of all reading
 

a	and	he	I
in	is	it	of
that	the	to	was

When you add the following 20 words, the 32 words together on average account for a third of all reading
 

all	are	as	at	be
but	for	had	have	him
his	not	on	one	said
so	they	we	with	you

 If you then add the following 68 words (making a total of 100 words) these words on average account for a half of all reading in English
 

about	an	back	been	before
big	by	call	came	can
come	could	did	do	down
first	from	get	go	has
her	here	if	into	just
like	little	look	made	make
more	me	much	must	my
no	new	now	off	old
only	or	our	other	out
over	right	she	see	some
their	them	then	there	this
two	up	want	well	went
were	what	when	where	which
who	will	your