Question

A rectangular page is to contain 24 sq. in. of print. The margins at the top and bottom of the page are each 1.5 inches. The margins on each side are 1 inch. What should the dimensions of the page be so that the least amount of paper is used

Answer 1

Answer:

Dimensions of page should be width of 6 inches and height of 9 inches

Step-by-step explanation:

Let x be the width of the printed part in inches

Let y be height of the printed part in inches.

Thus, Area of printed part; A = xy

And area of printed part is given as 24.

Thus, xy = 24

Making y the subject, we have;

y = 24/x

Now, the question says the top and bottom margins are 1.5 inches.

Thus, width of page = x + 1 + 1 = x + 2

And also the margins on each side are both 1m in length, thus the height of page will be:

y + 1.5 + 1.5 = y + 3

So area of page will now be;

A = (x + 2)•(y+3)

From earlier, we got y = 24/x

Thus,plugging this into area of page, we have;

A = (x + 2)•((24/x)+3)

A = 24 + 3x + 48/x + 6

A = 30 + 3x + 48/x

For us to find the minimum dimensions, we have to find the derivative of A and equate to zero

Thus,

dA/dx = 3 - 48/x²

Thus, dA/dx = 0 will be

3 - 48/x² = 0

Multiply through by x²:

3x² - 48 = 0

Thus,

3x² = 48

x² = 48/3

x = √16

x = 4 inches

Plugging this into y = 24/x,we have;

y = 24/4 = 6 inches

We want dimensions of page at x = 4 and y = 6.

From earlier, width of page = x + 2.

Thus,width = 4 + 2 = 6 inches

Height = y + 3 = 6 + 3 = 9 inches

So dimensions of page should be width of 6 inches and height of 9 inches