Vince borrows $900 to buy a couch. He will pay off the loan by paying 1.5% simple interest for 2 years. Vince incorrectly calculates the amount he will pay back using the expression below. 900 + 900(1.015 • 2) What is the correct amount Vince will pay back altogether? Explain the error in Vince’s expression.

To calculate the amount that Vince should pay back, we can use the formula of 
A = P + PRT 
where A is amount (unknown), P is principal ($900), R is rate of interest (1.5%).

Which in this case, Vince did follow the correct formula, but what he did wrong, it that he incorrectly changed the rate to a decimal. Instead, 1.5% should be 0.015 in decimal form.

So, the correct formula should be
A = 900 + 900(0.015x2)
A = 900 + 27
A = 927

So, the correct amount Vince should pay is $927.