Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

M and N are positive numbers. Is N > 0.06?

(1) When M + N is rounded to tenths digit the value is M
(2) N > 0.04

There are 2 variables (m,n) and 2 equations are given from the 2 conditions.
Looking at the conditions together, m and n has to be numbers like n=0.041, m=1.201, so that m+n=1.242
and n=0.041<0.06, so this answers the question 'no' and is sufficient, making the answer seem like (C).

However, this is a integer question, one of the key question. If we apply the common mistakes type 4(A),
Condition 1) If n>0.06, the tenth digit of m cannot be rounded up so this is 'no' and sufficient.
For condition 2, the answer is 'yes' for 0.07 but 'no' for n=0.05. This is insufficient as the range of the condition is not included in that of the question.
Therefore, the answer becomes (A).

For cases where we need 2 more equation, such as original conditions with “2 variables”, or “3 variables and 1 equation”, or “4 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 70% chance that C is the answer, while E has 25% chance. These two are the majority. In case of common mistake type 3,4, the answer may be from A, B or D but there is only 5% chance. Since C is most likely to be the answer using 1) and 2) separately according to DS definition (It saves us time). Obviously there may be cases where the answer is A, B, D or E.
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M and N are positive numbers. Is N > 0.06?

(1) When M + N is rounded to tenths digit the value is M
(2) N > 0.04

(2) N > 0.04
N could be = 0.05, 0.06, 0.07 not sufficient

(1) When M + N is rounded to tenths digit the value is M
so N should be .00 ---------------.49 so sufficient