Question: Sum of 4 Unknown Digits

Comment on Sum of 4 Unknown Digits

How about we use A=9, C=-1
greenlight-admin's picture

Nice idea, but there are no negative digits.
There are 10 digits altogether: 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9

To hard to do in a short time. Practice, practice and practice. Thanks.
greenlight-admin's picture

Agreed! It's a tricky question.

why cant c=2?
greenlight-admin's picture

Once we know that B = 1 and D = 0, it MUST be the case that C = 9

If it were the case that C = 2, then we must be able to assign different values for A, B, C and D so that the original sum works. Can you do that with C = 2?

Cheers,
Brent

Hey I didn't get why and how you assigned B=1 so in short I'm not able to grasp the whole idea of this type of question. Please explain.
greenlight-admin's picture

The question tells us that a 2-digit number PLUS another 2-digit number yields a 3-digit SUM.

Let's examine some examples of when this occurs:
50 + 80 = 130
29 + 72 = 101
99 + 99 = 198
63 + 71 = 134
18 + 85 = 103

Notice that, in all of these cases, the hundreds digit is 1.
In fact, in this situation, the 3-digit number will ALWAYS have hundreds digit 1.

For this reason, we know that B = 1

Does that help?

Cheers,
Brent

When you say, "In fact, in this situation, the 3-digit number will ALWAYS have units digit 1." did you mean 3-digit number will always have hundreds digit 1?
greenlight-admin's picture

Oops my bad. I changed my response above to have "hundreds" (not unit)

Thanks for the heads up!

My logic to remember:

The sum of any two 2-digit numbers can never exceed 198, so, the first digit of the sum must be 1.
greenlight-admin's picture

That's perfectly logical reasoning!

Hello brent,
Can you please let me know, where can I find more similar practice questions?

Hi dear Brent,
Could you please give us more than three questions of this type, at least 10 practice questions?
Thanks a ton

Thanks a ton, I appreciate that :)

What If a=7 b= 6 c=8 d=4

A+B+C+D=25

76
68
---
144
---
greenlight-admin's picture

Close but, those numbers don't meet the conditions of the question.
The sum must be BDD
Using your values, BDD = 644 (not 144)

Study Guide

The step-by-step Study Guide will help direct your studies and ensure that you cover everything that the GRE tests.

Test Day Mindset

As part of your preparation, work on adopting the proper mindset/attitude on test day. This will do wonders for your score. 

Free “Question of the Day” emails!