Why can't 3/7 be written as a terminating decimal

because it is a repeating decimal

https://en.wikipedia.org/wiki/Repeating_decimal
namely 3 * (1/7) where 1/7 is a repeater

because it is a repeating decimal

there is a group of 6 digits that repeats continuously

3/7 = .

because it is a repeating decimal

there is a group of 6 digits that repeats continuously

3/7 = .428571428571...

To explain why 3/7 cannot be written as a terminating decimal, we need to understand the concept of terminating decimals.

Terminating decimals are decimal numbers that have a finite number of digits after the decimal point. For example, 0.25, 3.6, and 12.345 are all terminating decimals because they have a specific number of digits after the decimal point.

When we calculate 3/7, we get the decimal representation of 0.428571428571... The pattern of repeating digits (in this case, 428571) indicates that the decimal is a repeating decimal. In other words, the digit sequence 428571 repeats infinitely.

To understand why this happens, let's perform the division manually:

0.428571428571...
--------------------
7 | 3.000000000000...

When we divide 3 by 7, we get 0 as the whole number part. The remainder is then multiplied by 10 to continue the division process.

4
-------
7 | 30.000000000...
28
-------
20

This process continues indefinitely, and we can see that the remainder never becomes zero. Therefore, the division never fully terminates, and the resulting decimal is a repeating decimal.

In conclusion, 3/7 cannot be written as a terminating decimal because it produces a repeating pattern after the decimal point.