Answer:
At the beginning of 6th month , Jeff will have in his account $ 520 .
Explanation:
At the beginning of 6th month , Jeff will have in his account,
$
= $
= $
= $
= $ 520
since, the $ 100 deposited at the end of 1st month earns interest for 4 months till the end of the 5th month, the $ 100 deposited at the end of the 2nd month earns interest for 3 months and so on till the last $100 deposited earns interest for '0' month.