"Interviewer gave me an assignment which due later on this week. "
Yea, I wonder why he gave you a week ... lots of stuff there ... and with that I also wonder if this is the normal procedure for this company's interview . Over the years I have seen some companies do intensive interviews to get ideas or answers on something they want to do or are trying to figure out how to do something cheaply ... and Never Hire anyone ... the people being interviewed are providing Free Consultation.
I have also never seen a company give someone a week to do some assignment either ... usually they question you and some make you take a test like "Prove-It" or "Brain Bench", etc. ... which I always decline ... and I don't take any goofy in-house tests either that some companies develop themselves ... I already have Real Certifications to present for a job.
The most I have seen is a major company here that wanted a write-up on: "How Do You Make a Peanut Butter Sandwich?" ... something you know that company Was Not working on and you mailed it in with your Resume ... and if it looked good, then they invited you in for an interview.
Check out the company on someplace like "Glassdoor" and see if they are there and what others have said about working for them and their interview process ... Legit or Scam.
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The flow depends on how detailed you want to get and land a job.
I'd probably start with the cost of doing this marketing promotion ... Vendor selection, how many cards to make, how many winners could there be (suppose they made 10,000 cards and everyone won $5 ?) ... was this an error or planned? would the promotion be worth it? There is your First Decision Point ... Continue or Forget it.
*** Remember to get the lawyers involved (legal department) for all the disclaimers on the scratch off cards ***
What advertising is needed to let this promotion to be known (paper, TV, Radio, etc). What will make people come ($5 won't make me go ... but Free Food might).
How are the winning numbers generated (software, pick from a hat, let the vendor generate numbers and give to you for validation).
Webpage development to validate a number and see if they won.
Do they have to come in to claim $5 or Is the person winning a current or new customer? Will a new customer actually proceed any further to get $5 (application for new account)?
If they are a current customer, update their account with $5 (database update - new modifications from the webpage validation).
If new customer (create account and add $5).
How can that $5 be used (can it be withdrawn as cash or only used as a credit to purchase store products).
You get the idea ... The process flows can go on for quite a bit ... I'm glad You are the one having fun.