In a box, there are $20$ non-defective and some defective bulbs. If the probability that a bulb selected at random from the box found to be defective is $\frac{3}{8}$ then, find the number of defective bulbs. 

The king and queen of diamonds, queen and jack of hearts, jack and king of spades are removed from a deck of $52$ playing cards and then well shuffled. Now one card is drawn at random from the remaining cards. Determine the probability that the card is a clover.

The king and queen of diamonds, queen and jack of hearts, jack and king of spades are removed from a deck of $52$playing cards and then well shuffled. Now one card is drawn at random from the remaining cards. Determine the probability that the card is a queen of a red card.

The king and queen of diamonds, queen and jack of hearts, jack and king of spades are removed from a deck of $52$playing cards and then well shuffled. Now one card is drawn at random from the remaining cards. Determine the probability that the card is a king of black card.

Some boys are playing a game, in which the stone thrown by them landing in a circular region given in the figure, is considered as win and landing other than the circular region is considered as loss. What is the probability to win the game? [Take $\mathrm{\pi }=3.14$]

Two customers Priya and Amuthan are visiting a particular shop in the same week (Monday to Saturday). Each is equally likely to visit the shop on any one day as on another day. What is the probability that both will visit the shop on the same day, in the lowest fraction form?

Two customers Priya and Amuthan are visiting a particular shop in the same week (Monday to Saturday). Each is equally likely to visit the shop on any one day as on another day. What is the probability that both will visit the shop on different days.  

Two customers Priya and Amuthan are visiting a particular shop in the same week (Monday to Saturday). Each is equally likely to visit the shop on any one day as on another day. What is the probability that both will visit the shop on consecutive days? 

In a game, the entry fee is $₹150.$ The game consists of tossing a coin $3$ times. Dhana bought a ticket for entry. If one or two heads show, she gets her entry fee back. If she throws $3$ heads, she receives double the entry fees. Otherwise, she will lose. Find the probability that she gets double entry fee.