Yesterday, my blog reminded me of this incident from seven years back when my friend from Singapore – Jyotsna – had pointed out that puzzles from my blog were being discussed in the classes of Singapore. And she asked me to post more.

So, here goes a fairly interesting puzzle:

Imagine a pharmaceutical company in a race to find a cure for coronavirus. It has come up with 1000 chemical formulas as potential anti-virus vaccinations. Those chemical formulas are sitting as solutions in 1000 different beakers in their lab.

However, only 1 of them is effective. In fact, it is supereffective. Even a small trace of it injected in a rat’s body will extinguish the virus within 7 days. The other 999 are of no use. They also know that you can mix those chemical formulas up and the resultant concoction will retain all the properties of the original formulas. Put simply, in a combination of solutions, if you have even a little of the effective formula, the whole combination is supereffective. Else, any combination of those other 999 solutions is totally useless.

One catch is that the pharma company has exactly 7 days to win the race to a vaccination. Which means it gets only one time to inject rats with the various combinations of the chemicals and see what happens by the 7th day.

As if that was not enough, there is way too much demand for rats – apparently lots of pharma companies are trying to do experiments for the vaccination.

Finally, they have to find out the exact solution with the effective chemical formula – there is enough manufacturing capability to make only one of those solutions in a scaled manner.

What is the minimum number of rats the company has to procure to conclusively prove which one of the chemical formula is the ultimate solution against the virus? How would they do the experiment?