How many diamonds are there on playing cards in a 52 card pack?

Question

John and Jacob are playing bets. John gives $10 to Jacob and Jacob deals four cards out of a normal 52-card deck which are chosen by him completely randomly. Jacob keeps them facing down takes the first card and shows it to John. John has a choice of either keeping it or looking at the second card. When the second card is shown to him, he again has the choice of keeping or looking at the third which is followed by the third card as well; only if he does not want the third card, he will have to keep the fourth card.

If the card that John is choosing is n, Jacob will give it to him. Then the cards will be shuffled and the game will be played repeatedly. Now you might think that it all depends on chance, but John has come up with a strategy that will help him turn the favor in his odds.

Can you deduce the strategy of John?

Answer 1

13 cards will have diamonds on it out of 52
According to standard 52-deck card :
Every card of diamond(or any) suit should have 4 diamonds(or heart or club or spade respectively)
With that every card from A till 10 will have same number of diamonds(or it's suit symbol) extra associated as the value number of that card,
I.e A should have 4+1 diamonds,
2 should have 4+2 diamonds,
3 should have 4+3 diamonds and so on till 10.
J,K,Q will have 4+2 diamonds each.
So, total diamonds = 4×13 + (1+2+3+....+10) + 2×3
= 52 + (10×11)/2 + 6
= 52+55+6
= 113