Estimating a single number, in isolation and without context, is a complete waste of time. It all comes down to the context of what needs to be done with the number.
If I had to add 15000 to 1 trillion, I would estimate it as 0.
If I had to add 15000 to 0.0000000001, I would use the number as given.
To the nearest ten thousand, 20000
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The answer depends on what you want to use the estimate for. If it is being added to 1 billion, I would estimate it as 0. If adding to 25000, I would estimate it as 15000 and if adding to 0.075, I would leave it as it is.
15000 = 15000/1
19% of 15000= 19% * 15000= 0.19 * 15000= 2850
110% of 15000= 110% * 15000= 1.1 * 15000= 16,500
750.5% of 15000= 0.5% * 15000= 0.005 * 15000= 75
30% of 15000 = 30% * 15000 = 0.3 * 15000 = 4500
17% of 15000 = 17% * 15000 = 0.17 * 15000 = 2550
1% of 15000 = 1% * 15000 = 0.01 * 15000 = 150
15000/1
32% of 15,000= 32% * 15000= 0.32 * 15000= 4,800