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A red kangaroo and a gray kangaroo weigh $$139\textasciitilde\text{kg}$$ altogether. The red kangaroo weighs $$35\textasciitilde\text{kg}$$ less than the gray kangaroo. How much does the gray kangaroo weigh? 
Overseas Competition->Knowledge Point->Word Problem Modules->Questions Involving Sum, Difference and Multiples->Problems Involving Sum and Difference
$$139-35=104$$  Red kangaroo: $$104 \div2 = 52$$  Gray kangaroo: $$52+35=87$$ 