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

 It is currently 13 Nov 2018, 12:25

### 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

## Events & Promotions

###### Events & Promotions in November
PrevNext
SuMoTuWeThFrSa
28293031123
45678910
11121314151617
18192021222324
2526272829301
Open Detailed Calendar
• ### Essential GMAT Time-Management Hacks

November 14, 2018

November 14, 2018

07:00 PM PST

08:00 PM PST

Join the webinar and learn time-management tactics that will guarantee you answer all questions, in all sections, on time. Save your spot today! Nov. 14th at 7 PM PST

# The number of consecutive zeros at the end of 77!x42! is

Author Message
TAGS:

### Hide Tags

Senior Manager
Joined: 18 Jul 2018
Posts: 377
Location: India
Concentration: Finance, Marketing
WE: Engineering (Energy and Utilities)
The number of consecutive zeros at the end of 77!x42! is  [#permalink]

### Show Tags

16 Sep 2018, 02:18
2
00:00

Difficulty:

45% (medium)

Question Stats:

56% (01:31) correct 44% (01:46) wrong based on 25 sessions

### HideShow timer Statistics

The number of consecutive zeros at the end of 77!x42! is

1) 9
2) 18
3) 24
4) 27
5) 29

_________________

When you want something, the whole universe conspires in helping you achieve it.

Manager
Joined: 13 Feb 2018
Posts: 135
Re: The number of consecutive zeros at the end of 77!x42! is  [#permalink]

### Show Tags

16 Sep 2018, 02:35
Trialing zeros depends on 2 and 5 couples

As 77!, as well as 42!, has more twos than fives, we have to get the number of fives. There always will be enough twos.

First of all find fives in 77!
The best approach is to divide 77 by $$5^x$$. where x is an integer and $$5^x$$ doesn't exceed 77. Second, we need only quotient of the division and ignore remainder. Third, we add the quotients. So:
$$\frac{77}{5^1}$$=15
$$\frac{77}{5^2}$$=3

In 77! we have got 15+3=18 Fives

The same with 42!
$$\frac{42}{5}$$=8
$$\frac{42}{25}$$=1

8+1=9

Expression 77!*42! will have 18+9=27 fives

Imo
Ans: D
Director
Joined: 20 Feb 2015
Posts: 797
Concentration: Strategy, General Management
Re: The number of consecutive zeros at the end of 77!x42! is  [#permalink]

### Show Tags

16 Sep 2018, 02:36
Afc0892 wrote:
The number of consecutive zeros at the end of 77!x42! is

1) 9
2) 18
3) 24
4) 27
5) 29

number of consecutive zeroes = number of 5*2 pairs
since number of 5 < number of 2
finding number of 5 will suffice

77/5 + 77/25 = 15+3 = 18
+
42/5+42/25 = 8+1 = 9

total = 27
D
Re: The number of consecutive zeros at the end of 77!x42! is &nbs [#permalink] 16 Sep 2018, 02:36
Display posts from previous: Sort by