Finding strings in a file using regex and grep in Linux -

i trying find proper regexes use grep command on file text.txt.

question

1. find occurrences of words in text have substring ad, bd, cd, dd, ed.

2. find occurrences of numbers > 100

3. find occurrences of numbers > 100 contain digit 0 or 5

my approach

1. grep -io '[a-e]*d' text

   prints words proper substrings, doesn’t print whole string/word.

   ad d d ed d d ed d d d d ed d d 

2. grep -io '[199][1-9]*' text

   i believe way off on regex, still prints correct result.

   1973 197 17775 

3. grep -io '[05][1-9]*' text

   this continuation of 2., don’t understand 2. part in 3., believe have string containing digit 0 or 5 correct.

   0 0 0 5 

a) find occurrences of words in text have substring ad, bd, cd, dd, ed.

grep -ow '.*\(a\|b\|c\|d\|e\)d.*' text 

or

egrep -ow '.*(a|b|c|d|e)d.*' text 

b) find occurrences of numbers > 100

grep -ow '[1-9][0-9][0-9]\+' text 

c) find occurrences of numbers > 100 contain digit 0 or 5

grep -ow '[1-9][0-9][0-9]\+' text | grep '\(0\|5\)' 

or

grep -ow '[1-9][0-9][0-9]\+' text | egrep '(0|5)' 

i'm using option -o output every match on it's own line , not whole line pattern found , option -w specifies before , after match should word boundary.