Big Ideas Math: Modeling Real Life, Grade 7
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Exercise 37 Page 275

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.

6 years

Practice makes perfect

If we deposit money in a savings account, the bank pays us interest for the use of our money. 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)Now, we made a deposit of $1525 in a savings account with an interest rate of 2.6 %= 0.026 and we earned $ 237.90 in interest. I= 237.90, p= 1525, r= 0.026 To calculate the time it takes the account to earn this interest, we will substitute these values into the simple interest formula and solve for t. Let's go!

I=prt
237.90=( 1525)( 0.026)t
237.90 = 39.65t
237.90/39.65 = 39.65t/39.65
6 = 39.65t/39.65
6=t
t = 6

The account earns $237.90 in interest in 6 years.