The coefficient of average rolling friction of a road road is $f_r$ and its grade is $+G\%$. If the grade of this road is doubled, what will be the percentage change in the braking distance (for the design vehicle to come to a stop) measured along the horizontal (assume all other parameters are kept unchanged)?

1. $\dfrac{0.01 \: G}{f_r+0.02 \:G} \times 100 \\$
2. $\dfrac{f_r}{f_r+0.02 \:G} \times 100 \\$
3. $\dfrac{0.02 \: G}{f_r+0.01 \:G} \times 100 \\$
4. $\dfrac{2f_r}{f_r+0.01 \:G} \times 100$