Aptitude - Problems on Numbers - Discussion
Discussion Forum : Problems on Numbers - General Questions (Q.No. 5)
5.
A two-digit number is such that the product of the digits is 8. When 18 is added to the number, then the digits are reversed. The number is:
Answer: Option
Explanation:
| Let the ten's and unit digit be x and | 8 | respectively. |
| x |
| Then, |  |
10x + | 8 |  |
+ 18 = 10 x | 8 | + x |
| x | x |
10x2 + 8 + 18x = 80 + x2
9x2 + 18x - 72 = 0
x2 + 2x - 8 = 0
(x + 4)(x - 2) = 0
x = 2.
Discussion:
43 comments Page 2 of 5.
Dipak said:
9 years ago
xy = 8
10x + y + 18 = 10y = x
9x - 9y + 18 = 0
x-y = -2
8/y - y = -2
So by solving above equation we get y = 4,
by putting y=4 in xy=8 so we get x = 2.
So the original no. is 10x+y = 24.
10x + y + 18 = 10y = x
9x - 9y + 18 = 0
x-y = -2
8/y - y = -2
So by solving above equation we get y = 4,
by putting y=4 in xy=8 so we get x = 2.
So the original no. is 10x+y = 24.
KRISHNA GUPTA said:
6 years ago
Lets number is xy;
Given xy=8; -----> (1)
10x + y + 18 = 10y+x.
y-x = 2 ----> (2).
Put y=8/x in (1)
So x^2+2x-8=0;
the root is 2,-4
x=2 so y is 4.
So the number is xy= 24.
Given xy=8; -----> (1)
10x + y + 18 = 10y+x.
y-x = 2 ----> (2).
Put y=8/x in (1)
So x^2+2x-8=0;
the root is 2,-4
x=2 so y is 4.
So the number is xy= 24.
(3)
Sudheer said:
1 decade ago
Products of 8 is 2*4, 4*2, 8*1, 1*8.
But he is telling by adding 18 to it the digits are reversed means 24+18=42.
24 is changed to 42. So, the answer is 24.
But he is telling by adding 18 to it the digits are reversed means 24+18=42.
24 is changed to 42. So, the answer is 24.
Vinod said:
10 years ago
Two digit number 10x+y.
xy = 8.
10x+y+18 = 10y+x.
x-y = -2.
(x+y)^2 = (x-y)^2+4xy.
= (-2)^2+4*8 = 36.
x+y = 6.
x-y = (-2).
x = 2.
y = 4.
Answer 24.
xy = 8.
10x+y+18 = 10y+x.
x-y = -2.
(x+y)^2 = (x-y)^2+4xy.
= (-2)^2+4*8 = 36.
x+y = 6.
x-y = (-2).
x = 2.
y = 4.
Answer 24.
Manojit said:
1 decade ago
Product of two digit means multiple of two digit.
Suppose two digit is x, y.
Then x*y=8
y=8/x
Now two digit is x, 8/x.
Then look the above problem.
Suppose two digit is x, y.
Then x*y=8
y=8/x
Now two digit is x, 8/x.
Then look the above problem.
Yash said:
5 years ago
Why X is taken as in the tenth position while 8/X taken as in-unit?
We could have taken X in unit and 8/X in tenth place?
Please explain me.
We could have taken X in unit and 8/X in tenth place?
Please explain me.
(5)
SK.Gopinath Siva said:
1 decade ago
Let me explain the simplest way.
The way is,
Let take two digit no as x and y.
x * y = 8.
xy + 18 = yx.
//xy = 8// .
8+18 = yx.
yx = 24.
The way is,
Let take two digit no as x and y.
x * y = 8.
xy + 18 = yx.
//xy = 8// .
8+18 = yx.
yx = 24.
Shanthi said:
1 decade ago
It is very simple. You can get answer from the options itself. 18+18=36 no. Not reversed. Tak 24+18=42 no. Reversed. 24 is reversed as 42.
Chandra said:
2 decades ago
There are only four two digit numbers whose product of the digits is 8. They are 18, 81, 24 and 42.
We can get easily 24 is the answer.
We can get easily 24 is the answer.
Sunil said:
8 years ago
The sum of five numbers is 18, their average is 3. 6 and their difference is 1. What are the numbers?
Can anyone tell me the answer?
Can anyone tell me the answer?
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