DS : FDP book #3 Test Case pg, 40

[SaniaS627]

I'm having a hard time understanding how the book tries to describe the logic of this question.


If x is +ve integer, what is the units digit of x?

1) the units digit of x/10 = 4
2) The tens digit of 10x = 5

for #1They test a few cases suchs as 45, and 46 where the units digit=4 (4.5 &4.6) but then they say if we had chosen 54, the units digit=5 so the stmt is not SUFF because it can give a diff answer if we pick a diff number for x.

2) They test two number 45 and 65 where the tens digit =5 (450, 650) but then they say if we had chosen 46 the tens digit = 6 so stmt will not be correct.
BUT in this case, they sa that YOU have to pick a value that makes the stmt (2) TRUE. Discard the case of 46 ?????

I am so confused because that logic of discarding the #46 for stmt 2 but NOT discarding the #54 for Stmt 1) makes no sense. Why didnt they discard 54 for stmt 1? Why are they NOT trying to prove stmt 1 Correct first?

Then they say that When you multiply x by 10, units digit becomes tens. if you know the tens digit of the new number is 5, then the units digit of the original number also has to be 5.

BUT we can say the same thing about stmt 1) when you divide x by 10, tens digit becomes units. if you know the units digit of the new number is 4, then the tens digit of the original number also has to be 4.

Correct answer is B

What am I not understanding ?

[RonPurewal]

hi,
please re-post your question in the correct folder (= "MPrep non-CAT math").
thank you.