In most simple problems like this, I prefer to solve it directly instead of using algebra. If the sum of the digits is 16, the digits can be 7 and 9, 8 and 8, or 9 and 7. So all we have to do is reverse the digits of 79, 88, and 97, to see which reversed number is 18 less than the original. But it should be pretty clear that we don't actually need to do that to all 3, because 97 is the only one that will get smaller by reversing the digits. I'm pretty sure by now that the answer is 97, but to be sure let's reverse the digits and check if the difference is 18: 97-79=18. Yep, 97's the answer!
This could also be solved using algebra, like they probably wanted you to do:
We'll use T for the tens digit and U for the units digit.
Given T+U=16 and 10T+U-18=10U+T, solve.
U=16-T
10T+16-T-18=10(16-T)+T 9T-2=160-9T
18T=162
T=9
U=16-9=7
So the original number was 97.
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2178
Possibility of two digit no whose sum is 10 Are 19,28,37,46,55,64,73,82,91 Add 72 to each no mentioned above output is 91,100,109,118,127,136,145,154,163 See first 19 and 91 Assume that two digit no as 19 reverse it 91 will come. The no 92 is 72 more than 19 So 19 is the original
78 Good guess, but 7 + 8 = 15, not 9; so that answer is incorrect. The correct answer is 54. 5 + 4 = 9 45 is 9 less than 54. * * * * * If the sum of the digits of a 2-digit number is 9, and if the order of the digits is reversed the new number will be a multiple of 9 different from the original. It could be bigger or smaller, and the difference could be 18 or 27. For example, 7+2 = 9 and 72 -27 = 45 (which is not 9 but a multiple of 9)
Possibility of two digit no whose sum is 9 18,27,36,45,54,63,72,81 Subract 9 with each no mentioned above output is 9,18,27,36,45,54,63,72 See after 4th comma 54 and 45. Reverse 54=45. now 45 is 9 less than 54. So the original no is 54
17
The number is 36
47 Impossible problem!
Find a four digit number whose digits will be reversed when multiplied by nine?
192
To total 17 the two digits must be 8 and 9! The original number was 98.
If the number with the digits reversed can have a leading 0 so that it is a 1-digit number, then 16. Otherwise 13.
45
An eight digit number with one zero cannot remain the same when its digits are reversed. It must have an even number of 0s.
"If the units digit and the hundreds digit of the number 513 were reversed..." 315 'find the sum of the original number and the new number." 513+315=828
A) If a number has two digits, then the sum of its digits is less than the value of the original two-digit number.
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