option premium doubled the moment i bought an option ?

Hi,
i have been trading in options for last few months and hence kind of a newbie.

yesterday i bought nifty 6400 November call option. its LTP was 17 when i was going to buy it.

when i completed the buy order, the options got purchased at 34 :annoyed:
1. before i bought there were already 10 lots trading on that day. i bought 10 lots. did this double the price ?

2. Also after i bought, the LTP went to 62. i got confused and so i sold one lot imme and it got sold at 20

Can someone explain this ?

Bro LTP means last traded price it does not mean u would get that rate too
I think u placed market order means w/o selling rate on the order placing window thats why u got highest buying rate and lowest selling rate where buyer is standing Hope I got u right

you mean someone had put a sell order limit of 34 ?

Yes you are right... Never ever put market order . Place your own bid and wait for it to be executed or If you are desperate to buy , check 5 best bids option and match with that. This is applicable in both selling and buying .

I have noticed that some time buyer/sellers put bid much less/higher than the last traded price specially in low volume counters or near 3:30 PM . Once I noticed(in 5 best bids) Few buyers had put bid to buy put of CANARA BANK at 5 , 1 when it was trading at 20. If by mistake any one sell in market order ..you can imagine what would have happened to that fellow.

So Always place limit order even if you want to buy/sell at premium/discounted price.