Remainders of 1, 2, 3, 4

Find the smallest whole number that when divided by 5 , 7 , 9 , 5, 7, 9, and 11 11 gives remainders of 1 , 2 , 3 , 1, 2, 3, and 4 4 respectively.


The answer is 1731.

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2 solutions

William Isoroku
Jan 16, 2015

Let the integer be n n . Then the question is as follows:

x = 5 a + 1 x=5a+1

x = 7 b + 2 x=7b+2

x = 9 c + 3 x=9c+3

x = 11 d + 4 x=11d+4

Multiplying these equations by 2 2 so that the remainders would also count by 2's, just as the divisors are:

2 x = 5 ( 2 a ) + 2 2x=5(2a)+2

2 x = 7 ( 2 b ) + 4 2x=7(2b)+4

2 x = 9 ( 2 c ) + 6 2x=9(2c)+6

2 x = 11 ( 2 d ) + 8 2x=11(2d)+8

Now add 3 3 to each equation so that the value of n n would be divisible by all the known divisors in the problem:

2 x + 3 = 5 ( 2 a ) + 5 = 5 ( 2 a + 1 ) 2x+3=5(2a)+5=5(2a+1)

2 x + 3 = 7 ( 2 b ) + 7 = 7 ( 2 b + 1 ) 2x+3=7(2b)+7=7(2b+1)

2 x + 3 = 9 ( 2 c ) + 9 = 9 ( 2 c + 1 ) 2x+3=9(2c)+9=9(2c+1)

2 x + 3 = 11 ( 2 d ) + 11 = 11 ( 2 d + 1 ) 2x+3=11(2d)+11=11(2d+1)

This means that 2 x + 3 2x+3 is the LCM of 5 , 7 , 9 , 11 5,7,9,11 , which is 3465 3465

So 2 x + 3 = 3465 2x+3=3465 and x = 1731 \boxed{x=1731}

wow, very nice solution :D, I just did de chinese remainder theorem, this solution is very awesome :D

Romeo Gomez - 6 years ago
Harshi Singh
Jun 2, 2015

@ABHISHEK Sahoo this is the question you are asking for

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