1/t=1/a + 1/b,
t =ab/(a+b),
5+20<a+b<8+24,
25<a+b<32,
5*20<ab<8*24,
100<ab<192,
100/25<ab/(a+b)<192/32,
4<ab/(a+b)<6
1/t=1/a + 1/b,
t =ab/(a+b),
5+20<a+b<8+24,
25<a+b<32,
5*20<ab<8*24,
100<ab<192,
100/25<ab/(a+b)<192/32,
4<ab/(a+b)<6