GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 20 Mar 2019, 00:41

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# If each term in the sum a1 + a2 + . . . + an is either 7 or 77...

Author Message
Intern
Joined: 26 Feb 2019
Posts: 1
If each term in the sum a1 + a2 + . . . + an is either 7 or 77...  [#permalink]

### Show Tags

Updated on: 26 Feb 2019, 19:58
1
00:00

Difficulty:

35% (medium)

Question Stats:

83% (01:36) correct 17% (02:34) wrong based on 6 sessions

### HideShow timer Statistics

How to solve this?

If each term in the sum a1 + a2 + . . . + an is either 7 or 77 and the sum equals 350, which of the following could be equal to n ?

a)38

b)39

c)40

d)41

e)42

Originally posted by prottenbucher on 26 Feb 2019, 16:00.
Last edited by u1983 on 26 Feb 2019, 19:58, edited 1 time in total.
edited ans
RC Moderator
Joined: 24 Aug 2016
Posts: 744
Concentration: Entrepreneurship, Operations
GMAT 1: 630 Q48 V28
GMAT 2: 540 Q49 V16
Re: If each term in the sum a1 + a2 + . . . + an is either 7 or 77...  [#permalink]

### Show Tags

26 Feb 2019, 20:00
If all 7, n =50 but then there are no 77.
If there is 1 77 , then that 77 accounts for 11 7s.
Hence total no of terms 39 (7s) +1 (77) = 40
Ans C
_________________

Please let me know if I am going in wrong direction.
Thanks in appreciation.

Intern
Joined: 28 Jul 2017
Posts: 1
If each term in the sum a1 + a2 + . . . + an is either 7 or 77...  [#permalink]

### Show Tags

26 Feb 2019, 20:04
1
Let’s say that there are x terms of 7 and y terms of 77 in the sum.
So, 7*x+77*y=350.
7(x+11y)=350
x+11y=50
Now, there is a limited number of values that y can take: 1, 2, 3, 4.
If y=1, then 39+11*1=50 --- x+y=40 (we have this answer choice).
If y=2, then 28+11*2=50 --- x+y=30 (we don’t have this answer choice).
If y=3, then 17+11*3=50 --- x+y=20 (we don’t have this answer choice).
If y=4, then 6+11*4=50 --- x+y=10 (we don’t have this answer choice).

Intern
Joined: 05 Oct 2018
Posts: 3
Re: If each term in the sum a1 + a2 + . . . + an is either 7 or 77...  [#permalink]

### Show Tags

26 Feb 2019, 20:31
1
a1+a2+a3......an = 350.
since the terms can be either 7 or 77 we take 7 common
7(a+11b) = 350
=> a + 11b = 50, where a is the number of terms equal to 7 and b is the number of terms equal to 77
Since the options are between 42 to 38, we know that b > 0.
(if b = 0, it would take 1*50 = 50 terms to get the sum 350)

take b=1
=> 50 - 11 = 39
1*39 = 39 (a=39)
Therefore number of terms = a+b = 1+ 39 = 40 (answer)
Increasing b would reduce the total number of terms below 38
check with b = 2
=> 50 - 22 = 28
=> Number of terms = 28 + 1 = 29(which is beyond the range of options). Therefore, we do not need to check the others
Math Expert
Joined: 02 Sep 2009
Posts: 53716
Re: If each term in the sum a1 + a2 + . . . + an is either 7 or 77...  [#permalink]

### Show Tags

26 Feb 2019, 21:12
1
prottenbucher wrote:
How to solve this?

If each term in the sum a1 + a2 + . . . + an is either 7 or 77 and the sum equals 350, which of the following could be equal to n ?

a)38

b)39

c)40

d)41

e)42

Discussed here: https://gmatclub.com/forum/if-each-term ... fl=similar

TOPIC IS LOCKED AND ARCHIVED.
_________________
Re: If each term in the sum a1 + a2 + . . . + an is either 7 or 77...   [#permalink] 26 Feb 2019, 21:12
Display posts from previous: Sort by