Bunuel wrote:

If the elevation above water level of a breaching wale is given by the expression −t^2 + 12t − 35 where t is the time, in seconds, after an observer begins watching, is the whale presently underwater?

(1) t < 8.

(2) t > 5.

A breaching whale is a whale leaping out of the water.

Elevation = −t^2 + 12t − 35

(1) t < 8

Let's notice what happens at exactly t = 8

Elevation = -(8)^2 + 12*8 - 35 = -3

It means the whale is under water at this time.

Put t = 7

Elevation = -(7)^2 + 12*7 - 35 = 0

So the whale is exactly at the surface at this time.

Put t = 6

Elevation = -(6)^2 + 12*6 - 35 = 1

The whale has a positive elevation at this time.

Let's find out what happens at t = 5

Elevation = -(5)^2 + 12*5 - 35 = 0

So the whale is exactly at the surface at this time.

We see what is happening here. The whale is exactly at the surface at t = 5, is out of water and then back in the water at t = 7.

Given that t < 8, the whale is underwater if t > 7 or t < 5. Not sufficient.

(2) t > 5

If t = 6, the whale is out of water but if t > 7, it is underwater. Not sufficient.

Using both, If t = 6, the whale is out of water but if t > 7, the whale is underwater. Not sufficient.

Answer (E)

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Karishma

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