Multiple conditions in One rule of Conditional Formatting

=and(a1<60,a1>49,b1<60,b1>40)

=and(a1<80,a1>60,b1<80,b1>60)

=and(a1<100,a1>79,b1<100,b1>79)

Thanks guys for your replies.
But i don't want to find the Minimum and put it in C2!!
Can it be defined in the rule of CF itself?
Also,how should i apply the same CF for all the rows below, WITHOUT defining them again and again for C2,C3,C4 and so on....