Answer :

voytek
As periods in mathematics we call groupings of large numbers (three-digits) usually separated by comma or space.

In this particular case we got two periods: 913 and 256.

Digits 913 are in the thousands period, while 256 in the units period.

Answer and Explanation: Starting from the right side we can see that 6 is on the Unit’s place, 5 lies on the Tenth place and 2 is in the hundred’s place. Every combination of three digits combine to make a period and we put a comma after every period. Starting from the right side the first three digits lie in the hundredth period and the next three digits will lie in the thousand's period so we can say that 913 lies in the thousand’s period.

I hope you understood the answer.