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Hello, I can help you solve this kind of questions;

Total number of counters 12

P(BL or R)=P(BL) + P(R)

P(BL or R)=3/12 + 4/12

P(BL or R)=7/12

Knowledge Required Beforehand:

1) Whenever you are asked to find the "Probability of an event A OR Probability of another event  B", just add the favorable outcomes of event A and event B.

Using this, in the question given above, the number of favorable outcomes = no. of black counters + no. of red counters = 3 + 4 = 7

2) One must also find the total number of possible outcomes.

For our problem total number of possible outcomes = number of Black Counters + number of red Counters + number of Blue Counters = 3 + 4 + 5 = 12.

3) P (E) = Number of Favorable Outcome ÷ Total Number of Possible Outcomes, where: P(E) stands for Probability of the event.

Actual Solution:

P (Black or Red Counter) =  Number of Black Or Red Counter ÷ Total Number of Possible Outcomes = 7÷12  = 0.58 (approximately).

Total no. of counters=12

Prob. of a black counter =3/12

Prob. of a red counter=4/12

And the probability of a counter being red and black is 4/12+3/12=7/12.

Probability = (Possibilities with right outcome) / (Total possibilities)

Possibilities with right outcome = "How many are 'black or red' "

Total possibilities = "How many counters in total"

Answer will be a fraction / decimal between 0 (never happens) and 1 (always happens).

Hope this helps.

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