If x=(10^10)-47, what is the sum of all the digit of x?
A. 40
B. 45
C. 50
D. 55
E. 80
*An answer will be posted in 2 days
Target Test Prep is 20% off right now!
Use code FLASH20
Available with Beat the GMAT members only code
MORE DETAILS
If x=(10^10)-47, what is the sum of all the digit of x?
This topic has expert replies
-
Max@Math Revolution
- Elite Legendary Member
- Posts: 3991
- Joined: Fri Jul 24, 2015 2:28 am
- Location: Las Vegas, USA
- Thanked: 19 times
- Followed by:37 members
Math Revolution
The World's Most "Complete" GMAT Math Course!
Score an excellent Q49-51 just like 70% of our students.
[Free] Full on-demand course (7 days) - 100 hours of video lessons, 490 lesson topics, and 2,000 questions.
[Course] Starting $79 for on-demand and $60 for tutoring per hour and $390 only for Live Online.
Email to : [email protected]
-
DavidG@VeritasPrep
- Legendary Member
- Posts: 2663
- Joined: Wed Jan 14, 2015 8:25 am
- Location: Boston, MA
- Thanked: 1153 times
- Followed by:128 members
- GMAT Score:770
It can be helpful to work with small numbers to establish a pattern.Max@Math Revolution wrote:If x=(10^10)-47, what is the sum of all the digit of x?
A. 40
B. 45
C. 50
D. 55
E. 80
*An answer will be posted in 2 days
(10^2) - 47 = 100-47 = 53. (Sum = 5+3)
(10^3) - 47 = 1000 - 47 = 953. (Sum = 9 + 5 + 3)
(10^4) - 47 = 10,000 - 47 = 9953. (Sum = 9 + 9 + 5 + 3 = 2*9 + 5 + 3)
Now we see a pattern. The number of 9's in the sum will be two less than the exponent value. And we always have the 5 + 3.
(10^10) - 47 --> Sum = 8*9 + 5 + 3 = 80, or E
