Some confusion related to probability

Question

3 company manufacturers 1000 scooters in a month. Plants A, B and C manufactures 500,300 and 200 resp. 90%,92% and 95% scooter are standard quality in these plants.

So what is the probability that a scooter selected at random is of stndard quality.

How to go about it?

Answer 1

Azhad

It's an expectation problem.

If you select a scooter at random : probability from A is 500/1000, probability that is standard is 0.90

B 300/1000, 0.92

C 200 / 1000 0.95

So expectation is 0.5 x 0.90 + 0.3 x 0.92 + 0.2 x 0.95 (you can calculate this).

You could also draw a tree diagram. First branch is the plant (3 branches), second branch is the quality (standard/non-standard) and find the probabilities at the end of the 2nd branches, and add together.

Mike

Answer 2

The total produced from plant A that are standard quality is 500(0.90) = 450.

The total produced from plant B that are standard quality is 300(0.92) = 276

The total produced from plant C that are standard quality is 200(0.95) = 190

That means the total produced in a month that are standard quality is 450 + 276 + 190 = 916

So 916/1000 are standard quality