A 2.5 kg pack of atta is 12% protein by weight. How many grams of protein does the pack contain?

The answer is asked in grams, so convert first: 2.5 kg = 2500 g. Then 12% of $2500=\frac{12}{100}\times 2500=300$ g. The trap in 0.3 g is working out 12% of 2.5 (which gives 0.3 **kg**) and then writing "g" on the end. 30 g comes from a slip in the kg → g conversion, and 250 g from using 10% instead of 12%.