# Rectangular Deck

• Sep 28th 2008, 10:31 PM
magentarita
Rectangular Deck
A homeowner wants to increase the size of a rectangular deck that now measures 15 feet by 20 feet, but building code laws state that a homeownercannot have a deck larger than 900 square feet. If the length and the width are to be increased by the same amount, find, to the nearest tenth, the maximum number of feet that the length of the deck may be increased in size legally.

My Work:

I let x = different values but the same for the width and length.

If x = 12, then width = 12 + 15 = 27 ft.

If x = 12, then length = 12 + 20 = 32 ft.

The 32 ft times 27 ft = 864 ft, which is close to 900 square feet but not over 900 square feet.

However, the answer is 12.6 not 12.

How do I get 12.6?

• Sep 28th 2008, 10:43 PM
Jhevon
Quote:

Originally Posted by magentarita
A homeowner wants to increase the size of a rectangular deck that now measures 15 feet by 20 feet, but building code laws state that a homeownercannot have a deck larger than 900 square feet. If the length and the width are to be increased by the same amount, find, to the nearest tenth, the maximum number of feet that the length of the deck may be increased in size legally.

My Work:

I let x = different values but the same for the width and length.

If x = 12, then width = 12 + 15 = 27 ft.

If x = 12, then length = 12 + 20 = 32 ft.

The 32 ft times 27 ft = 864 ft, which is close to 900 square feet but not over 900 square feet.

However, the answer is 12.6 not 12.

How do I get 12.6?

let x be the the number of feet we increase the length and width by, so the new length and width are (20 + x) and (15 + x) respectively

we want (20 + x)(15 + x) = 900

solve for x
• Sep 29th 2008, 12:39 AM
shailen.sobhee
I have a doubt here. The question says "by the same amount". This phrase can be interpreted in two different ways:

(1) By same amount : same increment. Example, both increase by 10 ft
(2) By same amount : by same percentage. (The the answer differs)

If I consider interpretation (2),

Final_length = Initial_Length * %total_percentage
Final_width = Initial_width * %total_percentage

The %total_percentage = $\frac{100 + percentage_ increase}{100}$

Let %total_percentage = x

Final_width * Final_length $\leq$ 900

20x * 15x $\leq$ 900
x^2 $\leq$ 3
x $\leq$ $\surd{3}$
x $\leq$ 1.73

Therefore increase in length = (1.73*20 -25)ft = 14.6, which is also a correct answer based on my reasoning.

You cannot work according to the answer, because in a test, you cannot anticipate the correct answer. You have to work for it.
• Sep 29th 2008, 12:51 AM
Jhevon
Quote:

Originally Posted by shailen.sobhee
I have a doubt here. The question says "by the same amount". This phrase can be interpreted in two different ways:

(1) By same amount : same increment. Example, both increase by 10 ft
(2) By same amount : by same percentage. (The the answer differs)

If I consider interpretation (2),

Final_length = Initial_Length * %total_percentage
Final_width = Initial_width * %total_percentage

The %total_percentage = $\frac{100 + percentage_ increase}{100}$

Let %total_percentage = x

Final_width * Final_length $\leq$ 900

20x * 15x $\leq$ 900
x^2 $\leq$ 3
x $\leq$ $\surd{3}$
x $\leq$ 1.73

Therefore increase in length = (1.73*20 -25)ft = 14.6, which is also a correct answer based on my reasoning.

You cannot work according to the answer, because in a test, you cannot anticipate the correct answer. You have to work for it.

i think they would say "percentage" or something like that if that's what they were after. it would be strange to interpret it otherwise really, that's the language they use here
• Sep 29th 2008, 10:36 PM
magentarita
ok
Quote:

Originally Posted by Jhevon
let x be the the number of feet we increase the length and width by, so the new length and width are (20 + x) and (15 + x) respectively

we want (20 + x)(15 + x) = 900

solve for x

I thank you.
• Sep 29th 2008, 10:37 PM
magentarita
ok
Quote:

Originally Posted by shailen.sobhee
I have a doubt here. The question says "by the same amount". This phrase can be interpreted in two different ways:

(1) By same amount : same increment. Example, both increase by 10 ft
(2) By same amount : by same percentage. (The the answer differs)

If I consider interpretation (2),

Final_length = Initial_Length * %total_percentage
Final_width = Initial_width * %total_percentage

The %total_percentage = $\frac{100 + percentage_ increase}{100}$

Let %total_percentage = x

Final_width * Final_length $\leq$ 900

20x * 15x $\leq$ 900
x^2 $\leq$ 3
x $\leq$ $\surd{3}$
x $\leq$ 1.73

Therefore increase in length = (1.73*20 -25)ft = 14.6, which is also a correct answer based on my reasoning.

You cannot work according to the answer, because in a test, you cannot anticipate the correct answer. You have to work for it.

I thank you for your input.
• Sep 29th 2008, 10:37 PM
magentarita
ok
Quote:

Originally Posted by Jhevon
i think they would say "percentage" or something like that if that's what they were after. it would be strange to interpret it otherwise really, that's the language they use here

I see what you mean.