Combi problem (with number theory I suppose?)

This is not relevant for jee but the first part was easy but the second one seems to elude me, case-working for small numbers didn't help either.

WhatsApp_Image_2025-06-15_at_11.00.21_abffb5c0.jpg

iTeachChem Helper•6/15/25, 5:36 AM

@Apu

iTeachChem Helper•6/15/25, 5:36 AM

Note for OP

+solved @user1 @user2...

+solved @user1 @user2...

to close the thread when your doubt is solved. Mention the users who helped you solve the doubt. This will be added to their stats.

SSirLancelotDuLac This is not relevant for jee but the first part was easy but the second one seem...

Opt•6/15/25, 5:36 AM

Ooohhh this looks fun

SirLancelotDuLacOP•6/15/25, 5:36 AM

Ikr. Randomly stumbled upon a nice book.

Opt•6/15/25, 5:37 AM

Which

Opt•6/15/25, 5:37 AM

OOpt Which

SirLancelotDuLacOP•6/15/25, 5:38 AM

I was tryna download 102 problems in combi, but accidentally wrote 50. So this is "50 challenging problems in combinatorics"

SirLancelotDuLacOP•6/15/25, 5:44 AM

Okay, using a calculator it seems 6 and 15 case works but seems hectic without the same :/

Opt•6/15/25, 5:45 AM

Yeah

Opt•6/15/25, 5:45 AM

You need to check 8r²-8r+1 for being a perfect square right?

OOpt You need to check 8r²-8r+1 for being a perfect square right?

SirLancelotDuLacOP•6/15/25, 5:46 AM

Making a quadratic in the total number of socks right?

Opt•6/15/25, 5:46 AM

Yup

OOpt Yup

SirLancelotDuLacOP•6/15/25, 11:30 AM

Tried the above, but didn't seem to work.

Opt•6/15/25, 11:33 AM

@SirLancelotDuLac this works ig?

rn_image_picker_lib_temp_43865b82-2391-48b3-81f2-565fa556a78f.jpg

Opt•6/15/25, 11:34 AM

b is no.of black
n is total

OOpt @SirLancelotDuLac this works ig?

SirLancelotDuLacOP•6/15/25, 11:35 AM

Plugging the answer in the original condition contradicts tho...

SSirLancelotDuLac Plugging the answer in the original condition contradicts tho...

Opt•6/15/25, 11:35 AM

Yeah idk what happened

SirLancelotDuLacOP•6/15/25, 11:37 AM

Hm...I don't see anything wrong tho :sweaty:

SSirLancelotDuLac Hm...I don't see anything wrong tho :sweaty:

Opt•6/15/25, 11:37 AM

Maths ain't mathing

SirLancelotDuLacOP•6/17/25, 2:47 AM

+solved @Opt

iTeachChem Helper•6/17/25, 2:47 AM

Post locked and archived successfully!

Archived by

@1075951732460376214 (1075951732460376214)

Time

June 17, 2025

Solved by

@763645886500175892 (763645886500175892)

Combi problem (with number theory I suppose?)

Similar Threads

Similar Threads

Similar Threads