GMAT Data Sufficiency (DS) | Re: Whenever martin has a restaurant bill with an amount between

Given:

Let A = amount of the bill, in which 10 < A < 99
Let T = tip
Let t(A) = tens digit of the amount, -> T = 2*t(A)

Question:

T > 15%(A)?
2*t(A) > 15%(A)?
2*t(A) >\frac{3}{20} *A?
\frac{40}{3} >\frac{A}{t(A)} ?

(1) 15 < A < 30
If A = 20, t(A) = 2
\frac{40}{3} >\frac{20}{2} ? Yes
If A = 29, t(A) = 2
\frac{40}{3} >\frac{29}{2} ? No
Hence, insufficient.

(2) T = 8
8 = 2*t(A)
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