If you are told only that you scored 80th percentile do you know from the description exactly how it wad calculated? explain

We know that there is no universal acceptance meaning of a percentile. When someone told you that you are in the 80th percentile, the meaning of that is you have achieved the lowest score that is greater than 80 percent of the score. It is calculated by using the formula     R = P/100 x (N + 1)

The cost of a hardcover book is $4

Step-by-step explanation:

Let the cost of one hard cover book be $x

Let the cost of one paper back book be $y

Nate bought 3 hardcover books and 7 paperback books and spent $29.50. This means that

3x + 7y = 29.5 - - - - - - - - - 1

Tia bought 2 hardcover books and 5 paperback books and spent $20.50. This means that

2x + 5y = 20.5 - - - - - - - - -2

Multiplying equation 1 by 2 and equation 2 by 3. It becomes

6x + 14y = 59

6x + 15y = 61.5

Subtracting,

- y = - 2.5

y = 2.5

Substituting y = 2.5 into equation 1, it becomes

3x + 7×2.5 = 29.5

3x + 17.5 = 29.5

3x = 29.5 - 17.5 = 12

x = 12/3 = 4