Number Theory. I think so its Not too Hard

Number Theory Level pending

A square has tens digit 7. What is its units digit???

7 8 6 9

2 solutions

Ramiel To-ong
Sep 19, 2015

nice solution everyone

Ajay Chandra
Apr 10, 2015

Suppose the unsquared number is N = N^1 ab where a is tens digit and b is its digit. = 100N^1 + 10a + b N = 10a + b(mod 100) N^2 = (20ab+b^2)(mod 100) As the 10's digit of N^2 is odd(7) The carry from b^2 to tens digit must be odd. Therefore, the unit digit of N is 4 or 6. Therefore, the unit digit of N^2 is 6...

i think first possible answer for this case is $74$ square

Harshi Singh - 5 years, 11 months ago

24 is the first possible answer.

Anshuman Singh Bais - 5 years, 10 months ago

oh yeah i forget to take that case even i forgot 26 square also thanks

Harshi Singh - 5 years, 10 months ago

@Harshi Singh – harshi i want to ask u a question that do u study in c square if u study in c square then in which batch do u study

sumit cooooool - 5 years, 10 months ago

@Sumit Cooooool – do u know me???yes i study in c square in R 1 race) batch are you also a csqarian @sumit cooooool

Harshi Singh - 5 years, 9 months ago

@Harshi Singh – is it ur real name i don't think so .......???? i guess ur realname is harshita singh

sumit cooooool - 5 years, 9 months ago

@Sumit Cooooool – correct but if I'm not wrong then your real name is Sumit gangwani

Harshi Singh - 5 years, 9 months ago

@Harshi Singh – wronggggg.....,,, my name is abhishek sahoo as i forgot the password if the older id in brilliant i had to make a new one using my pet name..... but whose in ur profile photo

sumit cooooool - 5 years, 9 months ago

@Sumit Cooooool – my real sister...but i also want to ask you a question why u behave like this ,earlier when you talked about c 2 gold medals then i have asked u a question and u didn't replied..and now u r again starting

Harshi Singh - 5 years, 9 months ago

@Harshi Singh – actually that was a blunder a ...a mighty mis conception i and mohit compared u as harshi singh of 8 th kcp batch now in spine she got 4 gold medals in last seminar of c square and gujan sir comented on her that she likes gold medals . ... ... .now when our misconception got cleared i just want to confirm that we were right or wrong..... if i disturbed u plz forgive me ..all the best of nmtc and i know ur going to be selected......

sumit cooooool - 5 years, 9 months ago

also i want to ask you whether you are giving RMO this year or not

Harshi Singh - 5 years, 10 months ago

Number Theory. I think so its Not too Hard

2 solutions

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