Final answer:
To determine the percentage increase, the increase in Miss Johnson's car fund is divided by the original amount and then multiplied by 100. The calculations show a 100% increase, which is option c).
Step-by-step explanation:
To calculate the percentage increase in Miss Johnson's car fund, you subtract the original amount from the new amount and then divide by the original amount. Finally, you multiply by 100 to get the percentage. In this case, Miss Johnson's car fund went from $225 to $450. The increase in amount is $450 - $225 = $225. Now, we find the percentage increase by dividing the increase in amount by the original amount: $225 ÷ $225 = 1. To find the percentage, we multiply by 100: 1 × 100 = 100%. So, the percentage increase in her car fund is 100%, which corresponds to option c).