The sum of the ages of a mother a father and their son is 100 years. Each of their ages is a multiple of 10 and the mother was 30 years old when her son was born. How old is the son?小儿子的数学题, 英语不算难. 爹妈和儿子的年龄之和是100, 三人的年龄都是10的倍数. 妈是在30岁时生的儿子.问儿子几岁?解: 设 [ ...阅读全文 ]