Solution:

There are multiple solutions to do so.
Solution1 :
Press 1
Press / (divide)
Press % (percent)
Press / (divide) .... this step may not require in all calculator.
Note: Three unique keys are '1', '/' and '%'

Solution2 :(My favorite)
Press 1
Press 0
Press 0
Press =
Note: Three unique keys are '1', '0' and '='

Solution:

5

Solution:

According to the given data,

6 x number of notebooks + 5 x number of notepads = 32

Here, we are sure that the number of notebooks and the number of notepads can only result in whole numbers. Thus, the respective values will be 2 and 4.

Solution:

20 units, 12 units & 15 units

As hard as it may sound, we have to just apply some basic algebraic equations to solve it.
Let the three sides be X, Y and Z. Now, the area of different surfaces is given:
X * Y = 240
Z * Z = 300
Y * Z = 180

Multiplying the obtained equations:
(X*Y) (X*Z) (Y*Z) = 240 * 300 * 180
X^2 * Y ^2 * Z^2 = 12960000
(X*Y*Z)^2 = 12960000
X*Y*Z = 3600

Now we know that X*Y = 240

Thus Z = 3600/240 = 15.

If we put the given values in the same manner, we get the three sides:
X = 20 units
Y = 12 units
Z = 15 units

Solution:

10 percent of student study all four subjects.

Solution:

Augustus and Joshua play all the three sports. Stacy plays none.

This is when we have assumed that girls do not play football at all. If by any means, the school has a girl's football league, all we know is that one of the three play no sports at all and the others play all the three.

Solution:

68

Explanation:
(9 * 7) + 5 = 68

Solution:

$16

Solution:

Quadratic

Explanation:

quad(4 wheeler)
+ rat
+ i (eye)
+ C

Solution:

glass + ceiling(Symbol)
= glass ceiling