1) Regarding normal puzzles,if your logical ability is good then you will be able to solve puzzles at that moment.You cant do much about it,do practice puzzles given in coaching classes' material.
2) Market Estimation goes like this.Suppose you have to estimate the market of pizza hut in a day in delhi.
Then you can approach:
Population of delhi*--> Percentage of people from differenr classes* (eg middle class high class).Now people from low class will not prefer eating pizzas.
So we are left with high class and Middle class.
Now you can talk about no of pizza huts in delhi (suppose one in 3 pin codes).So a total of 33 pizza huts(rough estimation).
Now talk that a normal pizza cost this much.and so on.
Also take into account wheter its an holiday or not,some special occasion or not.
They just want to check ur analytics,your performace wil be good if you will take into account maximum no of factors as it will minimise the error in the final estimation.
Some of market estimation you can practice:
1)Market of apple i-phone in delhi
2)Estimation of Por*n cds/dvds market in delhi
3)Pizza hut market estimation
4)No of cars/2-wheelers in delhi
5)No of cat aspirints in CAT 2008
Before going for an interview, remember the facts (population,poverty ratio,mortality rate etc etc ) by heart.Also you can bluff that you are making an estimation for ex: about population of delhi (but in reality u know it),this might fetch u more marks.
Rest I leave this on you
Do post your results
All the best
-Accenture07
Help
, rethinking leads to confusion 
and confusion leads to half hearted efforts 
which finally leads to half hearted results.
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