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Consider a paging system uses, TLB’s access time is 30 ns and memory access time is 200ns. If the effective memory access time is 150ns, what will be the hit ratio of TLB?
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In case of a TLB hit, memory access time is 230 ns (30 ns to search the TLB and 200 ns to access memory).

In case of TLB miss, memory access time is 430 ns (30 ns to search the TLB to find there is no page entry, 200 ns to first access memory to find the page-frame mapping and then another 200 ns to access the desired byte in memory).

Effective memory access time is obtained by weighted averaging of the two times:

Let $x$ be the TLB hit ratio. Then, $150=x*230+(1-x)*430 \implies 200x=280 \implies x=1.4$

Is the question correct? I think some values are incorrect. Even if we put $x=1$, the best possible EMAT is 230 ns.
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H= 1.4  ........... correct 

but 

 i have one another solution :-)

Let h1 be the hit ratio of TLB
150 = h1(30) + (1 – h1)(30 + 200)
= 30h1 + (1 – h1)(230)
200h1 = 80
h1 = 40%

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I think the above question is incorrect and EMAT should be 250 ns then the TLB hit ratio would be 90 percent.

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