Solve each problem. Simple InterestSimple interest varies jointly as principal and time. If $1000 invested for 2 yr earned $70, find the amount of interest earned by $5000 invested for 5 yr.

Key Concepts

Simple Interest Formula

The simple interest formula is given by I = PRT, where I is the interest earned, P is the principal amount, R is the rate of interest per year, and T is the time in years. This formula allows us to calculate the interest earned on an investment over a specified period, making it essential for solving problems related to simple interest.

Joint Variation

Joint variation occurs when a quantity varies directly with two or more other quantities. In the context of simple interest, it means that interest earned varies jointly with the principal amount and the time the money is invested. Understanding this concept helps in establishing relationships between different variables in the problem.

Proportional Relationships

Proportional relationships indicate that two quantities maintain a constant ratio. In this problem, the interest earned from different principal amounts and time periods can be compared using ratios. Recognizing these relationships is crucial for scaling the interest earned from one scenario to another, allowing for the calculation of interest for different investments.