Question 1079820
let $1000 be heads and $2000 be tails
For the first 3 months needs 3 heads or 1/8 probability.
More than $4000 means $5000 or $6000: the latter is 3 tails (1/8), the other is 2 tails and a head, or 3/8.  The probability is 1/2.
More than $3000 includes $4000, so it would include 2 heads and a tail, which is another 3/8, so that probability would be 7/8.