Divisblility q (1 Viewer)

[=)(=]

Prove 10a-2 is visible by 3 if 2a+1 is divisible by 3

 

[5uckerberg]

Wait wrong forum.

 

[Lith_30]

I don't think that statement is true in the first place.

say a=1 (assuming a is an integer) then 2(1)+1=3 which is divisible by 3.
but 10(1)-2=8 which is not evenly divisible by 3

idk if there is something other to this question or @=)(= copied it wrong

 

[=)(=]

Thats exactly in the form I got it in the entrance exam I sat, so therefore 10a-2 isn't divible by 3 right?

 

[Lith_30]

If it was 10a+2 then the statement would be true, but if you are sure that was the question you got then it is probably is wrong. At least I think.

 

[ExtremelyBoredUser]

probably a typo

 

[5uckerberg]

Thanks, now I see why I cannot solve it at all. All because of a typo. Very unfortunate.

 

[=)(=]

There was also this question a rombous has side length 29cm, if one diagonal is 2 cm less than the other what is the area of the rombous

 

[5uckerberg]

There was also this question a rhombus has a side length of 29cm if one diagonal is 2 cm less than the other what is the area of the rhombus

Okay, here is my approach, since we do not know the length of the diagonals we simply will start off with the fact that the lengths of the diagonals will be centimetres.

Remember a rhombus will give us 4 right-angled triangles. Thus we now find the half of respectively which is .

Using Pythag we will find that .

This will actually give us . Equalling where x can be 42 or -40 but we know that length can never be negative so therefore x which is the unknown length is 42cm. Now that this is in the cards the problem can be easily solved.

Now for all the Year 7-10s a rhombus is half of a rectangle. So therefore the area of the rhombus is simply a half of the area of a rectangle of 40cm and 42cm, which when calculating is just .

 

[=)(=]

Ohh i took that approach but they didn't allow calculators in the exam so I couldn't complete it which is quite annoying ahha

 

[5uckerberg]

No, you can do all this without a calculator. Quadratic equation, moving fractions.

 

[ExtremelyBoredUser]

I tried all ways of trying to prove its true but nothing worked, even contrapositive, tried a contradiction proof and it failed so either this is some genius q or its a typo (most likely latter).

10a + 2 seems like what it shouldve been like @Lith_30 mentioned

2a +1 = 3k
10a + 5 = 5(3k)
10a + 2 = 3(5k) - 3
10a + 2 = 3(5k-1)

hence divisible by 3.

unfortunate such a thing came up in ur entrance exam, hopefully u didnt spend too much time on it in the exam itself and u can try inquiring abt it now with the centre

 

[=)(=]

But I didn't have that much time

I tried all ways of trying to prove its true but nothing worked, even contrapositive, tried a contradiction proof and it failed so either this is some genius q or its a typo (most likely latter).

10a + 2 seems like what it shouldve been like @Lith_30 mentioned

2a +1 = 3k
10a + 5 = 5(3k)
10a + 2 = 3(5k) - 3
10a + 2 = 3(5k-1)

hence divisible by 3.

unfortunate such a thing came up in ur entrance exam, hopefully u didnt spend too much time on it in the exam itself and u can try inquiring abt it now with the centre

Bro I didn't see the last page till 5 mins and rushed it so I probs mis read the q which is quite unfortunate

 

[ExtremelyBoredUser]

But I didn't have that much time
Bro I didn't see the last page till 5 mins and rushed it so I probs mis read the q which is quite unfortunate

oh that could makes sense so yea the q mightve been 10a+2 but u didnt remember it correctly. its all goods because theres nothing much u can do now, only thing u can do is give urself a hard earned break (before year 11 starts!) and get back to the "grind" (if u wish not saying u have to but if i was in ur position).

ive had plenty of exams where ive went what the actual fk did i do and how could i fk this up this badly and everyone i met has the same exp. haha

 

[=)(=]

oh that could makes sense so yea the q mightve been 10a+2 but u didnt remember it correctly. its all goods because theres nothing much u can do now, only thing u can do is give urself a hard earned break (before year 11 starts!) and get back to the "grind" or whatever u fancy.

True still kicking myself over that silly mistake, now it's time to grind on league of legends and apex hahaha

 

[ExtremelyBoredUser]

True still kicking myself over that silly mistake, now it's time to grind on league of legends and apex hahaha

ah the HSC is a side thing, u know just drop an easy 99 (joke joke joke) for asian parents then can back to the real shit, LoL/apex is where its at. can respect.

 

[=)(=]

ah the HSC is a side thing, u know just drop an easy 99 (joke joke joke) for asian parents then can back to the real shit, LoL/apex is where its at. can respect.

Ahahahhaahha u play?

 

[ExtremelyBoredUser]

Ahahahhaahha u play?

nah used to but had to stop for the hsc because theyre wayy too addictive. all goods tho im ready to degenerate after the hsc lmao

 

[=)(=]

Ahhhh fair enough haahahhhaha

 

[5uckerberg]

Ahhhh fair enough haahahhhaha

I think we can bring this topic back up at the end of 2023.