Answer:
approximately 27 grams
Work Shown:
Half life formula
y = A*(0.5)^(x/H)
where,
A = starting amount = 30 grams
H = half life period = 90 years
x = number of years that pass by = 12
y = amount left over after x years
Let's plug the values for x, A and H into the formula to find y
y = A*(0.5)^(x/H)
y = 30*(0.5)^(12/90)
y = 27.3516746567466
y = 27 .... rounding to the nearest whole number
Step-by-step explanation:
12.09 - 8.30 = 3.79
The reason why her answer was wrong is because when the '2' gets slashed into a '1' during carry over, it would have been 11 - 8 = 3 instead of a 4. (the 1st column)
The error that Juanita made is that she made a computational error when subtracting.