It will rain today. Will it rain tomorrow?

Question

(1) If it does not rain tomorrow, then it will not rain today.
(2) If it rains tomorrow, then it will rain today.

sourse : Cambridge test 5

vikramjit_01 · Answer

A Verbal DS? Maybe this can be solved by the If X then Y approach, https://www.gmatclub.com/phpbb/viewtopic.php?t=14547

riverripper · Answer

I am going to say each one is sufficient on its own.

Reading the question you can accept the first statement as a fact that it is going to rain today. 

1) Since you know that today it is going to rain, that means it has to rain tomorrow because if it isn't going to rain tomorrow and can't rain today...which is goes against the statement of fact in the question.

2) Turn the statement around. If it rains today it will rain tomorrow. You know its raining today so that means tomorrow it will rain.

vidyasagar · Answer

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

Fig · Answer

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.

umbdude · Answer

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.

ethan_casta · Answer

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.

UMB · Answer

I 'm very confused 
OA is A.

Thank you all for hot discussion
best regards

UMB

vshaunak@gmail.com · Answer

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.

ethan_casta · Answer

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.

georgesanjay · Answer

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"   .

It will rain today. Will it rain tomorrow?

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