请教两个gre数学题,谢谢~Ifrandsarepositiveintegers,eachgreaterthan1,andif11(s-1)=13(r-1),whatistheleastpossiblevalueofr+s?a.2b.11c.22d.24e.2为什么我算出来没有正确答案?这个题如何解析?有没有简便

Question

请教两个gre数学题,谢谢~
If r and s are positive integers,each greater than 1,and if 11(s-1)=13(r-1),what is the least possible value of r+s?
a.2 b.11 c.22 d.24 e.2
为什么我算出来没有正确答案?这个题如何解析?有没有简便的计算方法?还是只能一个一个带入运算?
In a certain country, a person is born every 3 seconds and a person dies every 10 seconds. Therefore, the birth and death rates account for a population growth rate of one person every
A.10/3 sec B.30/7sec C.7sec D.35/3sec E 13sec
这个题不懂,请做详细步骤,谢谢啦~~

Answer 1

（s-1)=13/11*(r-1)
s-1要想为整数,r-1必须被11整除,则r-1最小=11,r最小=12
S最小=14
s+r=26
30秒内,增加了10个,死亡了3个
则30s,多了7人
现在算多1人需要几秒
30/t=7/1
t=30/7s