Question

There is a row of cars starting a motor car race.If the 3rd car after the middle car is in the 10th position.How many cars are there at the starting?

Answer 1

If there is the middle car we can find total number of cars as

$$N=2k+1$$

The position of the middle car is

$$k+1$$

The position of the 3rd car after the middle car is 

$$k+1+3=10$$

$$k=10-4=6$$

So,

$$N=2(6)+1=13$$