numbers op

[d0nw0ng]

if the units digital of the three digit positive integer k is not zero, what is the tens digit of k?

1) the tens digit of k+9 is 3
2) the tens digit of k+4 is 2

[ratindasgupta]

Statement 1. the tens digit of k+9 is 3
Since the units digit is not 0, even if the units digit is the lowest i.e. 1, adding 9 to the number will affect the tens digit. Hence the tens digit of k is 2. SUFF

2) the tens digit of k+4 is 2
If the units digit of k is 6 or greater, the tens digit of k+4 will be 1. But if it is between 1 and 5, then the tens digit will be 2. INSUFF.

Answer is A

[arocks]

The answer is A

Consider any three digit number which doesn't have the last digit as 0.

Stmt1 if you add 9 to the number the tens digit becomes 3.

So the tens digit of the number must be 2. Because if you add 9 to the units digit - 1 would get carried over and the tens digit will become 3.

For eg. lets say our number is 525, now if you add 9 to it you get 534.
You can try this for any three digit number but the tens digit has to be 2.

For eg. 521+9, 526+9, 921+9, 225+9.....

The importance of the unit's digit not being 0 is that - if the number was 520 and you added 9. you'll get 529....

>>The tens digit of k has to be 2. stmt1 is suff.

Stmt2 - the tens digit of k+4 is 2

Doesn't give a conclusive answer - lets say the number k is 524 and we add 4, we get 528.
But if the number k is 517 and we add 4 we get 521.
So adding 4 may or may not have an impact on the tens digit. Which is not the case if you add 9 (in that case 1 has to carry over)
>> we can't be sure of the tens digit of k. stmt2 is insuff.

Not sure if that was the greatest explanation...but hope it helps!