CO madeeasy 2019 Multi level cache

Question

please explain how hit ratio of L2 is taken as 0.5? instead of 0.9 as 10 misses are mentioned

is it like as 20 misses at levle 1 out of which only 10 missed at level 2, so 10 out of 20 (and not 100) hence 0.5?

Comments

Yes, the L2 misses will be out of the total number of missed that L1 made. Since L1 has twenty misses and out of that twenty misses, 10 are misses for L2.

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btw, the answer given is wrong it has to 36/7 as the value of x is 18/7