Binomial expansion approximation help please?

The first four terms of the series expansion in ascending powers of x of (1 - x)^1/3. I've got this as 1 - (1/3)x - (1/9)x^2 - (5/81)x^3... and I'm fairly sure it's right. However, the question then says "by taking x = 0.1, show that 900^(1/3) is approximately equal to 15641/1620. Any ideas?