Trina rounded to the nearest whole number to solve the expression eighteen point nine minus eleven point four. Her steps are shown below. Which statement correctly describes her error?
eighteen point nine minus eleven point four
eighteen point nine is approximately equal to nineteen and eleven point four is approximately equal to twelve, so
eighteen point nine minus eleven point four is approximately equal to nineteen minus twelve which is approximately equal to seven.
11.4 is approximately = to 11 NOT 12.
19 - 11 = 8.
Trina's error lies in the step where she rounds the numbers to the nearest whole number. To correctly round eighteen point nine to the nearest whole number, we would look at the decimal part, which is point nine. As the decimal part is greater than or equal to point five, we round the whole number up to nineteen, not down. Similarly, for eleven point four, we would round to eleven since the decimal part is less than point five. Therefore, when Trina rounds eighteen point nine to nineteen and eleven point four to eleven, her calculation of eighteen point nine minus eleven point four as seven is incorrect.
To correctly solve the expression, we subtract the numbers without rounding to the nearest whole number.
eighteen point nine minus eleven point four equals 7.5.