please help and explain all thinking
2006-09-14 18:04:57 · 19 answers · asked by Hockey Chick 3 in Science & Mathematics ➔ Mathematics
forgot the number has to be five digits
2006-09-14 18:14:34 · update #1
The first digit must be an even number, otherwise when reversed, it cannot be a multiple of 4.
So the first digit can be 2,4,6,8
However, if a number starting with 4,6 or 8 is multiplied by 4, you would end up with a number with an extra digit. Hence the number must start with a 2, and hence end with a 8
So the number is of the form 2()8, and there can be any number of digits in the brackets.
So try 208, 218, 2008, 2018, etc..
Upon reaching 2178, you get 8712, which happens to be the answer.
For a 5 digit number, its 21978 x 4 = 87912
2006-09-14 18:19:04 · answer #1 · answered by galford_sg 2 · 3⤊ 0⤋
Lets suppose its a 2 digit number
(10a+b) * 4 = 10b + a
So
10b + a = (4a+[[b*4/10]])*10 + b*4mod10
So a = b*4 mod 10
Since b varies from 0 to 9 then
a would equal 0,4,8,2,6,0,4,8,2,6 (i.e a is even) since a = b*4 mod10
b must equal a + [[b*4/10]]
Varying b over the 2nd part of the right part gives
1 = 4a + 0; a = 1/4(not possible)
2 = 4a + 0; a = 1/2(not possible)
3 = 4a + 1; a = 1/2 (not possible)
4 = 4a + 1; a = 3/4 (not possible)
5 = 4a + 2; a = 3/4 (not possible)
6 = 4a + 2; a = 1 (not possible)
7 = 4a + 2; a = 5/4 (not possible)
8 = 4a + 3; a = 5/4 (not possible)
9 = 4a + 3; a = 3/2 (not possible)
So at least for a 2 digit number it is not possible (other than 00)
2006-09-15 01:20:51 · answer #2 · answered by Anonymous · 0⤊ 1⤋
11
2006-09-15 08:01:39 · answer #3 · answered by Anonymous · 0⤊ 0⤋
11
2006-09-15 01:07:35 · answer #4 · answered by nazeer l 1 · 0⤊ 2⤋
Well, for a number to be same forwards and backwards you know it has to be 11, 22, 33, 44, 55, 66, 77, 88, or 99 or two digit numbers. Now check which one can be divided by 4. 44 can be divided by 4 so the answer is:
11
2006-09-15 01:06:20 · answer #5 · answered by Elim 5 · 0⤊ 2⤋
Thats a tough question, which everyone seems to have misunderstood here. I assume you mean that what number, if multiplied by 4, becomes the original number in reverse.
Its too bad it has to be 5 digits, because;
2178 x 4 = 8712
2006-09-15 01:22:59 · answer #6 · answered by iandanielx 3 · 1⤊ 0⤋
11
11 x 4 =44
2006-09-15 01:06:07 · answer #7 · answered by leo 4 · 0⤊ 2⤋
11 x 4 = 44 itz the same forward and backward Answer: 11
2006-09-15 01:06:44 · answer #8 · answered by Pearl 2 · 0⤊ 2⤋
some multiples of 11 i.e.
4*11=44
4*121=484
4*22=88
4*101=404
2006-09-15 01:11:24 · answer #9 · answered by azeem 2 · 1⤊ 2⤋
Zero
2006-09-15 03:00:56 · answer #10 · answered by Anonymous · 1⤊ 0⤋