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a and b are two positive integers that are not divisible by [#permalink]
06 Mar 2007, 00:31

00:00

A

B

C

D

E

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct
0% (00:00) wrong based on 1 sessions

a and b are two positive integers that are not divisible by 10, and the sum of the digits of the product of a and b is 1. Which of the following cannot be the remainder when |a-b| is divided by 10?

(I) 5
(II) 9
(III) 0

(A) I only (B) II only (C) III only (D) II and III only (E) I, II and III

Last edited by kevincan on 06 Mar 2007, 10:06, edited 1 time in total.

There are three numbers 1, 10, 100 can be product of a and b, and the sum of digits would be 1. Beyond 100 one of the numbers has to be divisible by 10.

1 = 1*1
10 = 2*5
100= 4*25

|1-1| = 0, remainder=0, when divided by 10
|2-5| = 3, remainder=3, when divided by 10
|4-25| = 21, remainder=1, when divided by 10

so the answer is (I) and (II). But do not see the choice with (I) and (II). Am I doing something wrong?

1 = 1*1 remainder is zero
10= 5*2 remainder is 3
100 = 25*4 remainder is 1
1000 = 125*8 remainder is 7
10000 = 625*16 remainder is 9
100000 = 3125*32 remainder is 3
and so on......

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