Felix and Marmalade are two cats. Together they weigh $$10\text{kg}$$.  Felix weighs $$4\text{kg}$$ less than Marmalade. How much does Marmalade weigh? 
Overseas Competition->Knowledge Point->Word Problem Modules->Questions Involving Sum, Difference and Multiples->Problems Involving Sum and Difference
$$F=M-4$$  $$m-4+M=10$$  $$M=7$$ 