Part of 27 pebbles is removed from on the desk by 2 persons in turn. A

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Part of 27 pebbles is removed from on the desk by 2 persons in turn. After removing by 2 persons, is the number of the remained pebbles an odd number?

1) One person removed 4 pebbles more than the other person removed.
2) The sum of the number of pebbles removed is 8


When you modify the question in the original condition, it becomes 27-(a+b)=odd?. Then there are 2 variables(a,b), which should match with the number of equations. So you need 2 equations. For 1) 1 equation, for 2) 1 equation, which is likely to make C the answer.
When 1) & 2), a=2, b=6 are derived, which makes 27-8=19=odd. It is yes and C is the answer. However, since this is an integer(hidden) question, which is one of the key questions, apply the mistake type 4. For 2), since a+b=8, 27-8=19=odd, which is yes and sufficient.
For 1), in a=b+4, a+b=b+4+b=2(b+2)=even is derived, which is yes and sufficient. Therefore, the answer is D. This is the mistake type 4(B) question.