Questions

Compressions and Rarefactions are characteristic of Longitudinal waves.

The direction of vibration of the particles is in the same plane as in which the wave is propagating. The particles vibrate back and forth, about their mean positions.

Athens is the capital of Greece

At least one black can be chosen in two ways from each box:
Now, probability of choosing at least one black ball from first box 

= 1/2 × [ (2C1× 2C1)/4C2 + 2C2/ 4C2 ]= 5/12

Probability of choosing at least one black ball from 2nd box
= 1/2 × [(4C1×12C1)/16C2 + 4C2/ 16C2] = 9/40

Final probability

= 5/12 + 9/40 = (50 + 27)/120 = 77/120

In direct marketing, there is a direct interaction of the customers with the seller without any intermediaries. Here, the role of the intermediaries is nil. The medium used is more direct using telephone, mail, internet where the seller can directly reach out to the consumer. Examples of such marketing include telemarketing, email, voicemail marketing, door-to-door selling etc. This kind of marketing is more time saving as the problem of distance which may otherwise exist between the buyer and seller is eliminated and is also cost effective as it minimizes commuting costs.