[경제성공학] Chapter 1. Foundations of Engineering Economy

경제성공학 김장호 교수님 수업 (19-1)

 

Decision Making

• Decisions are based on economic and noneconomic elements
• What actually happens might be differnt from our estimate, but our goal is to make good estimates
• The time frame of engineering economy is primarily future
• four essential elements
  • cash flow
  • times
  • interest rate
  • measure of economic worth for selecting an alternative

Time value of Money (화폐의 시간 가치)

• It explains the change in the amount of money over time that is owned or owed
• 돈을 빌릴 때, 돈을 빌려줄 때 
• Time value of Money is the most important concept in engineering economy

Interest

• shows the time value of money
• 돈을 빌려줄(투자) 때 interest is earned 
• 돈을 빌릴 때 interest is paid

 

Interest Rate = (시간당 발생한 이자 / 원금) * 100

• 원금에서 얼마나 늘었는지 비율

# interest = 현재 돈 - 원금  // OX문제가 나오면 interest rate인지 interest인지 확인하자

 

Rate of Return(ROR, 수익률)

• Interest rate is mostly referred to interest paid when borrowing money(돈 빌릴 때 주로 사용)
• 투자해서 얻은 interest는 보통 ROR이라고 적는다.(헷갈리지 말라고 구분하는 듯)
• in summary, interest rate paid and rate of return earned

Cash flows (1)

• amounts of money received or paid
• size(=the amount of money), timing(이자가 붙는 기간을 먼저 설정, 이자는 그 기간의 끝에 발생한다고 가정), and direction of cash flows are important 
• Timing : 
  • interest period를 설정
  • cash flow가 interest period의 끝에 발생한다고 가정

Cash flows (2)

• Cash inflows : receipts, revenues, incomes, savings('+' sign)
• Cash outflows : costs, expenses, taxes('-' sign)

Economic Equivalence

• 시간에 따라서 돈의 가치는 다름(이자와 time value 때문에)
• 시간이 달라도 돈의 가치를 비교할 수 있게 계산하는 것이 Economic Equivalence
• Economic equivalence considers both cash flow amounts and time
• Is a combination of interest rate and time value of money

Simple Interest

• 이자만 가지고 계산을 하는 것
• 이전에 발생한 이자에 대해서는 고려하지 않는다.
  it ignores any interest accrued in preceding interest periods
• simple interest = (principal)(number of periods)(interest rate)

Compound Interest(복리 이자)

• 대부분 복리 사용
• interest on interest
• accumulated in all previous peiods
• compound interest = (principal + all accrued interest)(interest rate)