Ram Kishore Bajpai asked: (The question is posted as such without rectifying errors.)
“Why is the time defined by distance traveled by light in vacuum 1/299,452,758?
Why does the people use a easier number such as 1/300,000,000? Why didn’t 1 second?”
It seems that you are confused a little.
The distance traveled by light in vacuum in 1/299,452,758 of a second is defined as one metre. This is because light travels 299,452,758 m in one second in vacuum.
The value 299,452,758 m/s is the speed of light calculated by various experiments and universally accepted standard.
But ordinary situations do not demand this much level of accuracy. If you correct the value 299,452,758 m/s to 1 decimal accuracy, you will get 3.0 x 108 m/s (3,00,000 m/s) and is used in ordinary calculations requiring one or two decimal places accuracy.