How many times in a day I should feed the pet fish in the tank?

Ive always fed our tropicals 1-2 times daily. Depending on type and size. Provided your not talking about salt water. If so, ask the place where you got them, as they are much more difficult to care for.

You can feed a few times a day as long as it's light feedings and they eat it all and the filter can handle the waste they put out due to more frequent feedings. If your not sure, less is better, you can even feed every other day. It is better than polluting the water which in turn will surely kill the fish.

I have two tanks at the moment, one with guppies, platies, a female betta, a male betta, an angelfish, and a pleco, that tank is fed twice a day, morning and night. My other tank is FULL of fry, it is fed up to 5-6 times a day, they are very very tiny feedings, and I clean the tank every second day so there is no left over food, but my babies won't starve. Also, when I place fry in the main tank I feed 3-4 times a day for about a week so the adults don't get hungry and start bugging the fry (and by that time there used to the little ones and there large enough to not be eaten). Honestly, you can feed as much as you like as often as you like as long as your ready to clean up all the left over food, so if you notice there is a lot of uneaten food try feeding less (and make sure you clean up the uneaten food). Remember a fish's stomach is only about the size of its eye.