Question

The Mexican Tetra is a tropical fish that requires a water temperature between 68 and 77 degrees Fahrenheit, inclusive. An aquarium is heated 8 degrees so that a Tetra can live in it. What temperatures could the water have been before the heating?

Answer 1

The temperature of the water could have been between 60 and 69 degrees Fahrenheit(inclusive) before the heating.

Explanation

Suppose, the temperature of the water before the heating was $x$ degree Fahrenheit.

The aquarium is heated 8 degrees so that a Tetra can live in it. So, the current temperature of the water $=(x+8)$ degree Fahrenheit.

Given that, Tetra requires a water temperature between 68 and 77 degrees Fahrenheit, inclusive. So.....

$68\leq x+8\leq 77\\ \\ 68-8\leq x\leq 77-8\\ \\ 60\leq x\leq 69$

Thus, the temperature of the water could have been between 60 and 69 degrees Fahrenheit(inclusive) before the heating.