Big Ideas Math: Modeling Real Life, Grade 7
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6. Simple Interest
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Exercise 26 Page 270

Use the simple interest formula I=Prt, where I is the interest, P the principal, r the annual interest rate, and t the time in years.

$ 1770

Practice makes perfect
If we borrow money from a bank, we pay the bank interest for the use of their money. Similarly, if we open a savings account, the bank deposits extra money on this account as interest. To calculate the interest I, we use the simple interest formula. I= P r t, where... I& = Interest P& = Principal r& = Annual interest rate t& = Time (in years) We know that we take a loan of $1500 with an annual interest rate of 9 %. We want to calculate the amount we pay for the loan after 2 years. Keep in mind that 9 % is written in decimal form as 0.09. P= 1500, r= 0.09, t= 2 To calculate the interest, we will substitute these values into the simple interest formula and evaluate the right-hand side.
I=Prt
I= 1500( 0.09)( 2)
I=135(2)
I=270
After 2 years, the interest accrued is $270. The total amount we pay for the loan is the sum of the loan and the accrued interest. $ 1500+ $ 270=$ 1770 The amount we pay after 2 years is $ 1770.