So we have the formula: 
where
is the distance in kilometers
is the petrol in liters
is the petrol consumption in kilometers per liter
We now for our problem that <span>David drove a distance of 187 km, so </span>
. We also know that he used 28 liters of petrol, so 
. Lets replace those values in our formula to find the petrol consumption:
Now, remember that are some rules to determine the number of significant figures in a number:
1. Non-zero digits are always significant figures.
2. A zero between tow significant figures is always a significant figure.
Applying those tow rules we realize that has 6 significant figures, whereas has three significant figures and only two. In mathematical operations with significant figures, the answer should be given with the same significant figures as the number with least significant figures involved in the operations. In our case, that number is , and has two significant figures, so our answer should have 2 significant figures. To give our answer with 2 significant figures, we are going to round it:
We can conclude that the patrol consumption of David's vehicle is 6.7 kilometers per liter.
where
We now for our problem that <span>David drove a distance of 187 km, so </span>
Now, remember that are some rules to determine the number of significant figures in a number:
1. Non-zero digits are always significant figures.
2. A zero between tow significant figures is always a significant figure.
Applying those tow rules we realize that
We can conclude that the patrol consumption of David's vehicle is 6.7 kilometers per liter.