# Homework Help: Carbon Dioxide Output Percentage Change

1. Nov 4, 2013

### shubu

1. The problem statement, all variables and given/known data
Question: If petroleum used in transportation were replaced by electricity generated by coal, what would be the percentage change in carbon dioxide output?

Refer to the following diagrams for values:

Given Information:
• Petroleum has an efficiency rating of 1/4 in transportation.
• Coal that is burned to produce electricity has 1/3 efficiency.
• Petroleum has 2/3 the carbon footprint of coal.
• Switching to coal means: using less of a fuel; fuel has higher carbon footprint.

2. Relevant equations
$Percentage \ change = \frac{Initial - Final}{|Initial|}$

3. The attempt at a solution
$Percentage \ change = \frac{1170 - 1180}{|1170|} \\$
$Percentage \ change = -0.56\%$

2. Nov 5, 2013

### haruspex

I don't know which numbers you fished out of those table to arrive at 1170 and 1180, but you do not need those tables at all for this question.
Suppose you need X units of transport energy. How many units of petrol would you need for that? What would be the number of CO2 units produced? Do the same calculation for coal.