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UMB
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IF A =>B THEN -B=> -A (contrapositive),

but -A =/> -B , hence

1) -R(TOMM)=> -R(TODAY) => R(TODAY) => R(TOMM) : SUFF.


2) R(TOMM)=> R(TODAY) => -R(TODAY) => -R(TOMM) (C/P)

(does not imply) =/> -{-R(TODAY)} => -{-R(TOMM)}

(does not imply) =/> {R(TODAY) => R(TOMM)} : INSUFF
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To me, I'm going with (E) :)

Let A and B events be:
o A: Rain today
o B: Rain tomorrow

IF A THEN B ?

From 1
IF not(B) THEN not(A)

That means B implies something on A. But, we cannot have a rule to say IF not(A) THEN not(B). Actually, if not(A), THEN not(B) or B :). And so, we are even lesser able to conclude on IF A THEN B.

INSUFF.

From 2
IF B THEN A

It's similar here. It's always B that impacts/implies something on A. But we cannot reverse it and say something like IF A THEN B.

INSUFF.

From 1 & 2
It's the same. We sum up 2 conditions influencing A by what happens in B. But we cannot reverse these conditions.

INSUFF.
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UMB
It will rain today. Will it rain tomorrow?

1) If it doesn't rain tomorrow , then it will not rain tday.

2) If it rains tomorow , then it will rain today.

sourse : Cambridge test 5

plz, with explanation.


Not sure how to explain this one with formulas, but I will have to go with E. Both statements tell you what will happen to today depending on what will happen tomorrow, but they don't tell you what will happen tomorrow based on what happens today. Combining them yields the same result. Therefore, we can't really tell what will happen tomorrow if it will rain today. Sort of counter intuitive.
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I believe this is B.

1. means: if it does not rain today => then it will not rain tomorrow.

but this too is possible: if it rains today => then it will not rain tomorrow.

so this is insufficient because we get a yes and no.

2. means: if it rains today => then it will rain tomorrow

the question gives us it will rain today. so we know it will rain tomorrow.

Therefore B.
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I 'm very confused
OA is A.

Thank you all for hot discussion
best regards

UMB
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This is a CR -
If X happens Y will happen.
It interprets - If Y doesn't happen, X doesn't happen.
So answer is 'A'

You can refer to HongHu's notes on 'If X, then Y' type of questions in CR.
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UMB, don't worry about it too much. People make mistakes in books and it goes unnoticed sometimes.

Just move on to other similar problems.
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My answer would be"A". Here's my explanation.

IT WILL RAIN TODAY. IT HAS TO RAIN TODAY. COS THE QUESTION SAYS SO.

NOW..

Statement 1:
If it DOESN'T rain tomorrow , then it will NOT rain today.
Since from the question we know that it WILL and HAS TO RAIN today, this means that considering Statement 1 also, it HAS TO RAIN tomorrow. Hence SUFFICIENT.

Statement 2:
If it rains tomorrow , then it WILL rain today.
BUT. It doesn't mean the other way round. ie., From this statement alone you can't say that if it rains today it will rain tomorrow. Hence INSUFFICIENT.

HENCE "A".

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