Data of activity is as follows:

(Reference for data : https://youtu.be/GlUZGUQKmKQ )

Toss (hr)	Radioactive nuclei
0	240
1	117
2	64
3	34
4	13
5	6
6	4
7	0

1. Estimation of time of first 4 half life

Estimation of time up to 1st half life:

In 1st toss or 1hr the number of nuclei changed from 240 t0 117 ....for half life it must be around 120 nuclei

so estimated value of 1st half life = (120/123)hr= 0.975hr (approx.)

Estimation of time up to 2nd half life:

In 2nd toss or 2hr the number of nuclei changed from 117 t0 64 ....for half life it must be around 60 nuclei

so estimated value of 2nd half life = 1hr+(60/64)=1.938 hr (approx.)

Estimation of time up to 3rd half life:

In 3rd toss or 3hr the number of nuclei changed from 64 to 34 ....for half life it must be around 30 nuclei

so estimated value of 2nd half life = 2hr +(30/34)hr= 2.882hr (approx.)

Estimation of time up to 4th half life:

In 3rd toss or 3hr the number of nuclei changed from 34 to 13 ....for half life it must be around 15 nuclei

so estimated value of 2nd half life = 3hr +(15/17)hr= 3.882hr (approx.)

What is the reasoning behind the process to get these estimated values? Why do you do the following, (120/123)hr= 0.975hr (approx.) to get the estimated value of the 1st half-life, for example?