Pentagon Geometry

[Videoorchard]

Hey,

The below question is take from guide 3, chapter 4, Problem set, Question 2.

Q:
A pentagon has 3 sides with length x and two sides with length 3x. If x is 2/3 of an inch, what is the perimeter of the pentagon?

My approach:
Pentagon perimeter= x+x+x+3x+3x=9x.

Here X is defined as 2/3 of "an inch". One inch=2.5..Therefore value of x=(2/3)*(2.5)=1.667.

Ans: 9x1.667=15

P.S: The value "of an inch" i.e 2.54,.

I know i have interpreted the question differently, What went wrong?

[n00bpron00bpron00b]

A pentagon has 3 sides with length x and two sides with length 3x. If x is 2/3 of an inch, what is the perimeter of the pentagon?

My approach:
Pentagon perimeter= x+x+x+3x+3x=9x.

Here X is defined as 2/3 of "an inch". One inch=2.5..Therefore value of x=(2/3)*(2.5)=1.667.

Ans: 9x1.667=15

P.S: The value "of an inch" i.e 2.54,.

All your steps are correct except for one thing

1 inch = 2.54 cm
x = (2/3) of 2.54 = 1.6933333333... cm
9x = 9(1.6933333...) cm
= 15.2397 or approx 15 "cm" and not inches

convert 15 cm back into inches you get 5.90551 inches or 6 inches

[Videoorchard]

Hi Noob,

Thank you for answering! I have a follow up questions.

#1. What other standard measurement values do you think we should remember for the test? KG? Pounds? Clearly. i wouldn't have been able to solve the problem, if i dint know the value of 1 inch=2.5! :)

[n00bpron00bpron00b]

#2. What other standard measurement values do you think we should remember for the test? KG? Pounds? Clearly. i wouldn't have been able to solve the problem, if i dint know the value of 1 inch=2.5! :)

Well, I am not sure about the types of unit conversion one is expected to memorize. Having said that, I haven't yet encountered any problems where my unit conversion knowledge was tested. Hopefully, the test makers should provide us with a conversion scale (if unit conversion is a part of problem solving). Tommy, please correct me if I am wrong.

But you are expected to remember conversions concerning time and day.

#1. The question, does not specify the form in which the answer has to be in. cm or inches? Or is it just that, the perimeter is always measured in inches? (Unless explicitly specified)

Or is it just that, the perimeter is always measured in inches?

No No never assume. It all depends on the units used/mentioned in the problem.

The question, does not specify the form in which the answer has to be in. cm or inches?

The problem statement states the following: "If X is 2/3 of an inch" (i.e. 2/3 of 1 inch) = 2/3 * 1 inch = 2/3 inch (conversion is not required here)

-> It is perfectly fine to convert but then make sure you reconvert the final answer back into inches (answer is required in inches) - tedious way though :)

[tommywallach]

Great explanations from Noob. That said, I don't understand why you switched into cm at all here...the question is about inches. As Noob said, all conversions are given except for times (24 hours in a day, 365 days in a year), so you don't need to know anything! : )