Aptitude - Problems on Numbers - Discussion

How can solve like this manner 8+18 = 24?

8+18 = 26. It's wrong. The product of the number is 8 not that number.

First we have to check with the options then only we find answer easily.

Here the first condition is that the multiple of that two digit number is 8.
Then we check all the options. Given four options satisfying the 1st condition.

Now go to 2nd condition, i.e if 18 is added to that two digit number the answer will be reversed.
So we can check through all the options then we get 24 is the correct option.

i.e 2*4 = 8.
24 + 18 = 42.

Hence the 2 conditions are satisfied.

Let's not look into the options to solve this. Let's solve from the scratch--
The product of 2 digits is 8:-

1 * 8 = 8
2 * 4 = 8
4 * 2 = 8
8 * 1= 8.

So, the number has to be any of the above-given numbers i.e 18 or 24 or 42 or 81.

Now, add 18 to all the above 4 numbers, only 24 will be reversed after adding 18. => 24 = 42 (reversed).

So, 24 is the answer.

Two digits=x & y so two digit no = 10x+y.
Product of digits is x*y = 8.

So (10x+y)+18 = 10y+x.
i.e x-y = -2......(1).
as x*y=8 so x = 8/y.

Hence equation (1) becomes 8/y-y = -2......(2).
Solving equation(2) we get y = 2.

Putting y=2 in equation (1) we get x = 4.
So the two digited number xy = 42.

So please tell me how answer comes to 24.
Please correct me if I am wrong?

Can anyone explain it in another way?

Answer is absolutely 24. I agree.

Hi @Gopinath.

How 8+18 = 24?

I think its 26.

Could anyone please provide the shortcut method?

I can't understand. Please explain in a simple way.

What is unit, ten digit and product.