If a = 2.4d7, and d represents a digit from 0 to 9, is d greater than

Question

If a = 2.4d7, and d represents a digit from 0 to 9, is d greater than 4 ?

(1) If  a  were rounded to the nearest hundredth, the new number would be greater than  a .
(2) If  a  were rounded to the nearest tenth, the new number would be greater than  a .

chetan2u · Answer

If a = 2.4d7, and d represents a digit from 0 to 9, is d greater than 4 ?

(1) If  a  were rounded to the nearest hundredth, the new number would be greater than  a .
 Irrespective of value of d, when a is rounded to hundredth place, the increase/decrease would depend on THOUSANDTH'S digit, which is 7 here. Thus the answer will always be greater than the original. 
So a can be anything from 0 to 9.
Insuff

(2) If  a  were rounded to the nearest tenth, the new number would be greater than  a 
 When a is rounded to tenth place, the increase/decrease would depend on HUNDREDTH'S digit, which is d here.  
If d is 0-4, a will decrease that is it will become 2.4..
But If d is >4, a will increase that is it will become 2.5..
Here it increases, so d>4.
Suff

B

CareerGeek · Answer

(1) If  a  were rounded to the nearest hundredth, the new number would be greater than  a 
--> Possible values of d = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9} -->  Insufficient

(2) If  a  were rounded to the nearest tenth, the new number would be greater than  a 
--> Possible values of d = {5, 6, 7, 8, 9} -->  Sufficient

Option B

if8 · Answer

I know the correct answer is B, but I think statement two is not suff because d could be 4. If d is 4 and you round to the nearest tenth then you will first round to the nearest hundreth (which if d is 4 it will become 5) and then rounding to the nearest tenth would yield a greater number. Even in statement (2), d could be 4 or 5 so... NOT SUFF. I would love to understand where I am wrong. Thanks

chetan2u · Answer

When you round to tenth, you round off directly to tenth. You do not round off to hundredth and then to tenth. 
So when you look at 2.447 and round off to nearest tenth, you look at what is there after tenth digit. 
It is 4, which is less than 5.
So 2.447 will become 2.4

For example 24445 when rounded to thousands will become 24000. But if you start rounding off from units digit. 
24445=24450=24500=25000

kc1020758 · Answer

Hi the thousandth is 7 so it won't round off to hundredth then to tenth? If d is 4, then 2.447 will be 2.5?

chetan2u · Answer

No, the logic is that particular number is closer to which rounded off position. 
So 2.447 is closer to 2.4 and not 2.5

Thus, you look at only 4 vs 5 or 47 vs 50

bumpbot · Answer

Automated notice from GMAT Club BumpBot: 

A member just gave Kudos to this thread, showing it’s still useful. I’ve bumped it to the top so more people can benefit. Feel free to add your own questions or solutions.

 This post was generated automatically.

If a = 2.4d7, and d represents a digit from 0 to 9, is d greater than

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards