Approximation: In the 4th paragraph, they said that "some 3000 singaporean men will....". The word some tells us that not exactly 3000 men will go but the exact number was rounded up to 3000.
Exact: In paragraph 1, they said that it is the 45th anniversary of the National Service. There were no other words that stated it was estimated.
I think that they rounded the numbers up to the nearest whole number.