Aptitude - Problems on Numbers - Discussion


In a two-digit, if it is known that its unit's digit exceeds its ten's digit by 2 and that the product of the given number and the sum of its digits is equal to 144, then the number is:

[A]. 24
[B]. 26
[C]. 42
[D]. 46

Answer: Option A


Let the ten's digit be x.

Then, unit's digit = x + 2.

Number = 10x + (x + 2) = 11x + 2.

Sum of digits = x + (x + 2) = 2x + 2.

(11x + 2)(2x + 2) = 144

22x2 + 26x - 140 = 0

11x2 + 13x - 70 = 0

(x - 2)(11x + 35) = 0

x = 2.

Hence, required number = 11x + 2 = 24.

Abc said: (Jul 5, 2010)  
how did u get 10x here

Mamta said: (Dec 23, 2010)  
confusing... can it be little more simplified

Bharathi said: (Feb 7, 2011)  
How unit digit is x+2 ?

Gupta said: (Feb 12, 2011)  
In the question it is clearly mentioned that units digit is 2 more than tens digit, then by observing the options only in 24 units digit(i.e.4 ) is more than 2 with tens digit(i.e.2).

Kranth said: (Feb 25, 2011)  
Confusing in the answer. There is not clearence.

Karthi said: (Feb 28, 2011)  
It is confusing please explain about 10x.

Soumya said: (Apr 25, 2011)  
Explanation about 10x
eg:123 means 100+20+3
in question its given tat unit's digit exceeds its ten's digit by 2 ,so units place is x+2 n tens place is 10x....

Naresh said: (Jun 10, 2011)  
Its not the case of confusing..its the case of time consuming...just check the options only two options may give the answer..24 and 46... now apply the second condition given in the problenm to these two options

24*(2+4)=144.. so this is the correct answer

Sandeep said: (Sep 9, 2011)  
Nice explanation naresh.

Ashmis said: (Sep 19, 2011)  
I just divided the 144 with the options. 144 is completely divided by 24 so that is the answer.

Indu said: (Nov 30, 2011)  
Please tell me why we do not take 10x+y here. Please sing 10x+y.

Venkat said: (Jan 4, 2012)  
If option A is correct according to naresh why not C, as it is same to a when we add up ?

Shikha said: (Feb 6, 2013)  
I don't get this step.

Sum of digits = x + (x + 2) = 2x + 2.

Why we added x instead of 10x to (x+2).

Avdhesh said: (Feb 11, 2013)  

We want the product of digit (ie. 24) and its sum (ie 2+4) = 144.
And for option C number is 42 doesn't satisfy the condition.

Avdhesh said: (Feb 11, 2013)  

Hey if we add 10x to (x+2) we will get that number. And when we add x to (x+2) we get the sum so. Hope I clarify a bit.

Posubabu said: (Aug 31, 2013)  
Let the ten's digit be x.

Then, unit's digit = x + 2.

for Example: Take Number 56.

Here unit digit is 6, ten's digit is 5, Then Number = 50(since its 10th digit)+6 = 56.

Hence in the above case: Number = 10x+ (x+2) = 11x+2.

The remaining same explained by indiabix.

Nupur said: (Jan 18, 2014)  
How did 11x2+13x-70 produces (x-2)(11x+35) factors?

Shakthi said: (Apr 4, 2014)  
Multiply a term(11) and c term (-70) = -770.

Find two numbers that when multiplied equal the number (-770) and add up to be the b term (13).

The numbers be -22 and 35.

Now write this as,

11x2-22x+35x-70 = 0.

11x (x-2) +35 (x-2) = 0.

The factors are x-2 and 11x-35.

If I'm wrong, please explain me.

Amrith said: (Aug 18, 2014)  
First mutiple 11* -70 which gives product = -770 and sum = 13.

Next factorise 770 number ,u will get 2*5*7*11...in this series try to make combination such that sum should be 13 and product should be -770.

The combination which we get is by trial and error, is 5*7=35 and 2*11=22, hence we choose 35 and -22 to satisfy p=-770 and sum=13,

Next substitute in equation,

(x-2)(11x+35) = 0.
Hence we get x = 2 and y = x+2 = 4.

Sudharshan said: (Aug 10, 2015)  
Find Two digit number which is 4 times of digits sum and 2 times of digits multiplication.

Rohan said: (Sep 5, 2015)  
Dear experts,

Please solve the following problem:

In a two-digit, if it is known that its unit's digit exceeds its ten's digit by 2 and if 18 is added with the number then the digits exchanges their position. Find the number with explanation.

Here's the answer 24, but I need algebraic explanation. Thanks.

Ayesha said: (Dec 30, 2015)  
How x=2 and y=x+2=4 came?

Anjali said: (Aug 24, 2016)  
Kindly explain it in any another method, I could not understand it.

Basavraj said: (Aug 30, 2016)  
Well said. Your explanation is good @Naresh.

Anjali said: (Sep 6, 2016)  
Correct answer @Naresh.

Akash said: (Sep 26, 2016)  
The simple method is to check the option.

Options B and C are wrong because of their option B] difference is not 2 and option C] unit digit is greater than 2. So this is neglected.

Now remaining option is 24 checks it 24 * (2 + 4) = 144 is true then it's a right answer.

Shiwani said: (Oct 29, 2016)  
Why we added x instead of 10x to (x+2)?

Nisha said: (Feb 24, 2017)  
How did you factorise the equation?

Please help me to solve it.

Naina said: (May 4, 2017)  

Can anyone tell me, Why we can't take 10x at ten's place and Y at an unit place?

Pratyasha said: (Jun 28, 2017)  
Because a 2-digit number is represented as 10x+y.

Moti Chavan said: (Jul 10, 2017)  
Yes, right @Pratyasha.

The 2 digit number is represented as 10x+y. But by taking like this I'm not getting answer.

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