Two balanced dice are rolled simultaneously. Then,the probability that the sum of numbers on the dice is $13$ is ..............

In a packet of $500$ screws,$80$ screws are defective. Find the probability that a screw selected at random from the packet is non-defective. (in $/25$)

Two balanced dice are rolled simultaneously. Then,the probability that the sum of numbers on the dice is $7$ is ............

If you toss a coin $6$ times and it comes down heads on each occasion,can you say that the probability of getting a head is $1$? Give reasons.

There are $5$ white,$7$ red,$4$ black and $2$ blue identical balls in a box. One ball is selected at random from the box. Find the probability that the ball is not blue.

Three balanced coins are tossed simultaneously. Find the probability of receiving at least two heads.