Looking at the solution explanations, they are understandable, but extremely long. You don't have time to calculate 10 steps of complicated divisions if you're low on time, there must be a faster way to find the answer.
The way you can
solve this within a minute:
--
What answers are
NOT possible?: A, B, C; --> not divisible by 4.
Now you are left with
D or
E, guessing here would be a
50% chance of success if you're low on time, better than the original 20%.
Option E seems a bit too high, so going with option D is the better bet.
If you have time to calculate, do an
estimation instead of precise math down to the last integer:
Test option
D simple and fast:
2560 * 1.25^4 is more easily calculated in the head as:
year 0: 2500 (rounding down to make head-math faster) -->
1/4 of 2500 is (exactly) 625, so in year 1 we have 3125;
1/4 of 3125 is (roughly) 800, so in year 2 we have 3925;
1/4 of 3925 is (roughly) 1000, so in year 3 are at 4925,
1/4 of that is (roughly) 1250, so in year 4 we are at
roughly 6250 (!)
If you want, you can also test answer E first and see that its much higher than 6250, in which case the only option will be
D.
This is for those who are not math-wizzes.
Hope this helped.