How can i grow weight of OBJECT randomly between 0.1-0.5% of it's current weight C++

So i have class platypus and function EAT which grows weight of platypus .i want weight to grow randomly between 0.1--0.5 % of platypus current weight. For example if i have platypus which weighs 10 kg i want EAT function to grow it's weight by 10*random between(0.1%--0.5%). PLEASE HELP