Elena finds it very difficult to remember a long string of numbers so she tries to memorize three numbers at a time. later she is able to repeat the numbers correctly because she grouped the numbers into more manageable groups of three. this is an example of

Chunking

Explanation:

Chunking refers to the act of gathering small individual information into several groups in order to address the shortage of space in our short term memory.

For examples , let's say that Someone's phone number is '87610989'. In order to memorize it ,.Most people will find it easier to chunk that information and remember it as 8761 - 9089