A kilogram is a measure of mass, not of weight, and so 30 maths books cannot possibly weigh 3 or 30 kilograms just as they cannot weight 3 or 30 minutes, or 3 or 30 metres.
About 30 kilograms.
30 - 80 kg.
It will weigh 30, thirty kilograms .
Willow Smith weighs 30 kilograms.
About 30 to 35 kilograms
A pint of 30 percent calcium chloride weight 0.7426 kg
Different sizes have different weights. Around 30 pounds is average.
30 kilograms = 66.14 pounds.
13.6 kilograms are 30 pounds.
30 pounds = 13.61 kilograms.
You can just use a set of weigh scales.
75% of 30 kilograms is 22.5 kilograms.