It is not decidable.
See, if there is a T.M. T1 which is accepting atleast 100 strings, then there must be a T.M. T2 which is accepting atleast 200 strings. T1 and T2 are doing the same jobs but they are complement to each other, thus they are related. Here, complement is like what T1 can do T2 cant do, so T2 cant accept a set of atleast 100 strings. So, it is undecidable ( Rice’s 1st theorem ).
Even if u cant understand the Rice’s theorem part, u can go with the definition of REC and R.E. languages. See, we know for REC languages, the halting turing machine would say yes or no to a problem and for R.E. languages we know that the T.M. will say yes, no or loop. Recursive languages are like the honest ppl who say yes or no after getting proposed and Recursively enumerable languages are like the unpredictable people who can say yes, no or keep u in a loop after getting proposed.
So, for T1 ( paragraph after first lyn), it is accepting atleast 100 strings. But suppose I make the value very large to make it realistic, suppose the turing machine is accepting set of atleast k strings. So, we give a related T.M., then one string, it wont accept, then 2 strings it wont accept and so on……… moral of the story is it is not halting and it wd go on and on. Because the value of k can be 10^10000000. So, the testing wd go on and on. Here u r taking the value 100 but I am taking a large value for making it realistic. In other words, we should be concerned abt the language and not the value.
So, as per definition it is undecidable.
Now for Rice's 2nd theorem to check semidecidability.
Suppose there is a TM 1 dat accepts atleast 100 strings and there is TM 2 dat accepts atleast 50 strings. Accepting atleast 50 strings is doing da job of accepting atleast 100 strings. Thus subset work is done here. So it is not semi decidable.
It is lyk as I told previously u r borrowing gate books from library and ur frnd is borrowing algo and db books frm library. Both of u r doing 2 different work so u both r doing complentary work. But while focussing on ur own work u r doing ur frnd's work too becoz borrowing gatee books is including books for algo and db. Thus the situation becomes not even semi decidable.