Writing code for three tasks
Ruby, 1356 1268 * 3 = 3804 bytes

if File.file?(?b)
s='P3
50 50
255
'
d=e=0
[153,44,6,1,42,1,6,1,42,1,6,1,42,1,6,1,42,1,6,1,42,1,6,1,42,1,4,40,5,1,4,1,1,1,36,1,5,1,4,1,1,1,36,1,5,1,4,1,1,1,36,1,5,1,4,1,1,1,36,1,5,1,4,1,1,34,3,1,5,1,4,1,34,1,3,1,5,1,4,1,34,1,3,1,5,1,4,1,34,1,3,1,5,1,4,1,34,1,3,1,5,1,4,1,34,1,3,1,5,1,4,1,34,1,3,1,5,1,4,1,34,1,3,1,5,1,4,1,34,1,3,1,5,1,4,1,34,1,3,1,5,1,4,1,34,1,3,1,5,1,4,1,34,1,3,1,5,1,4,1,34,1,3,1,5,1,4,1,8,31,5,1,4,1,8,1,25,1,9,1,4,1,8,1,25,1,9,1,4,1,8,1,25,1,9,1,4,1,8,1,25,1,9,1,4,1,8,1,25,1,9,1,4,1,8,1,25,1,9,1,4,1,8,1,25,1,9,1,4,1,8,37,4,1,34,1,14,1,34,1,14,1,34,1,14,1,34,1,14,1,34,1,14,1,34,1,14,1,34,1,14,1,34,1,14,1,34,1,14,1,34,1,14,1,34,1,14,36,63].map{|n|n.times{s+=[" 255 255 255"," 0 0 255"][d];s+=$/if (e+=1)%50==0};d=1-d}
File.write 'blue.ppm',s
elsif File.file?(?a)
puts [["","Mary had a ","little lamb",?,,?,,"Its fleece was white as snow"],["And ","everywhere that ","Mary went",?,,'',"The lamb was sure to go"],["","It followed her to ","school one day",'','',"Which was against the rules."],["","It made the children ","laugh and play",?,,'',"To see a lamb at school"]].map{|a,b,c,d,e,f|[a+b+c+d,c.capitalize+', '+c+d,b.capitalize+c+e,f]*$/}*"

"
`touch b`
else
1971.times{|i|$&gt;&lt;&lt;"#{i} "if i.to_s.chars.map(&amp;:to_i).reduce(:+)%17&lt;1}
`touch a`
end


To keep track of the invocation, I'm creating an empty file a on the first run and an empty file b on the second run.


The first program uses a certain property of the numbers.
The second program uses a bunch of reusable parts of the verses, but that currently only saves 100 bytes over naively printing the entire thing.
The third program currently uses just a simple run-length encoding. I'll look into actually encoding the path of the line later.