Last visit was: 11 Jul 2025, 14:03 It is currently 11 Jul 2025, 14:03
Close
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
Your Progress

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
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Close
Request Expert Reply
Confirm Cancel
User avatar
Pdirienzo
Joined: 13 Jul 2018
Last visit: 28 Nov 2020
Posts: 6
Own Kudos:
270
 [196]
Given Kudos: 15
GMAT 1: 650 Q47 V33
GMAT 1: 650 Q47 V33
Posts: 6
Kudos: 270
 [196]
4
Kudos
Add Kudos
192
Bookmarks
Bookmark this Post
Most Helpful Reply
avatar
iPrasad
Joined: 11 May 2018
Last visit: 30 Jun 2022
Posts: 25
Own Kudos:
87
 [63]
Given Kudos: 132
Location: India
50
Kudos
Add Kudos
13
Bookmarks
Bookmark this Post
User avatar
ScottTargetTestPrep
User avatar
Target Test Prep Representative
Joined: 14 Oct 2015
Last visit: 11 Jul 2025
Posts: 21,091
Own Kudos:
26,139
 [12]
Given Kudos: 296
Status:Founder & CEO
Affiliations: Target Test Prep
Location: United States (CA)
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 21,091
Kudos: 26,139
 [12]
11
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
General Discussion
User avatar
MahmoudFawzy
Joined: 27 Oct 2018
Last visit: 20 Feb 2021
Posts: 661
Own Kudos:
2,068
 [4]
Given Kudos: 200
Status:Manager
Location: Egypt
Concentration: Strategy, International Business
GPA: 3.67
WE:Pharmaceuticals (Healthcare/Pharmaceuticals)
Posts: 661
Kudos: 2,068
 [4]
3
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
\(\frac{20}{2^5} = \frac{1}{2^m} + \frac{1}{2^n}\)
\(\frac{5}{2^3} = \frac{1}{2^m} + \frac{1}{2^n}\)
\(5 = \frac{2^3}{2^m} + \frac{2^3}{2^n}\)
\(5 = 2^{3-m} + 2^{3-n}\)


now 5 can be the sum of two pairs of integers (0,5),(1,4),(2,3)
it can't be (0,5) because there is no valid value for x when \(2^x = 0\)
it will be difficult to deal with (2,3) because finding x when \(2^x = 3\) is difficult without a calculator.
by trying (1,4) pair,
if \(2^{3-m} = 1 = 2^0\), then \(3-m = 0\) and \(m = 3\)
if \(2^{3-n} = 4 = 2^2\), then \(3-n = 2\) and \(n = 1\)

so \(m*n = 3\)

note that there is no one unique value for (m,n) pair (as shown in the graph), however, the line pass through the (3,1), (1,3) points.
Attachments

Untitled-1.png
Untitled-1.png [ 40.45 KiB | Viewed 26063 times ]

User avatar
Staphyk
Joined: 20 Mar 2018
Last visit: 30 Jan 2022
Posts: 467
Own Kudos:
Given Kudos: 149
Location: Ghana
Concentration: Finance, Statistics
GMAT 1: 710 Q49 V39
Products:
GMAT 1: 710 Q49 V39
Posts: 467
Kudos: 372
Kudos
Add Kudos
Bookmarks
Bookmark this Post
20/(2^5)=1/2^m + 1/2^n
20/(2^5)=2^n+2^m/(2^m*2^n)
20(2^m*2^n)=(2^n+2^m)2^5
2^2*5(2^m*2^n)=(2^n+2^m)2^5
5(2^m*2^n)=(2^n+2^m)2^3
Now the only way the LHS will equate the RHS is when m=3 ,n=1 or when n=3 ,m=1
5(2^3*2^1)=(2^1+2^3)2^3
Now ,5*2=(2^1+2^3)
So m*n =3
Ans is B


Posted from my mobile device
avatar
kumarankit01
Joined: 13 Oct 2018
Last visit: 25 Feb 2019
Posts: 73
Own Kudos:
81
 [12]
Given Kudos: 6
Location: India
GPA: 3.1
WE:Information Technology (Computer Software)
Posts: 73
Kudos: 81
 [12]
12
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Here are my two cents.

20/32 = 5/8

= (1+4)8 = 1/8 +4/8
= 1/8 + 1/2

= 1/2^3 + 1/2^1

SO by comparing both side

we get m=3 and n=1

so mn = 3

I could not write full soultion in this due to typing overhead.

Please award kudos if helpful

Posted from my mobile device
6
Kudos
Add Kudos
3
Bookmarks
Bookmark this Post
here is how I approached this question:
step 1 : express the numerator as a sum of powers of denominator (2 in this case)
\(20 = 16 + 4 = 2^4+ 2^2\)

step 2: replace the above value in the equation
\(\frac{2^4+2^2}{2^5} =\frac{1}{2^m} + \frac{1}{2^n}\)

this gives:
\(\frac{2^4}{2^5}+\frac{2^2}{2^5} = \frac{1}{2^m} + \frac{1}{2^n}\)
step 3: solve for m and n

\(\frac{1}{2^1}+\frac{1}{2^3} = \frac{1}{2^m} + \frac{1}{2^n}\)

hence, m*n = 3, Option (B)
User avatar
BlueRocketAsh
Joined: 11 Oct 2019
Last visit: 28 Aug 2020
Posts: 76
Own Kudos:
Given Kudos: 2
Posts: 76
Kudos: 12
Kudos
Add Kudos
Bookmarks
Bookmark this Post
\(\frac{20}{2^5}=\frac{1}{2^m}+\frac{1}{2^n}\)
\(\frac{5}{2^3}=\frac{1}{2^m}+\frac{1}{2^n}\)
\(5=\frac{2^3}{2^m}+\frac{2^3}{2^n}\)
\(5=2^(^3^-^m^)+2^(^3^-^n^)\)

Only way this can be is
\(4+1=5 \)

Therefore (3-m)=2 and (3-n)=0 or (3-m)=0 or (3-n)=2
(m,m) = (1,3) or (3,1)

\(mn=3*1=3\)
User avatar
Kritisood
Joined: 21 Feb 2017
Last visit: 19 Jul 2023
Posts: 492
Own Kudos:
1,217
 [1]
Given Kudos: 1,090
Location: India
GMAT 1: 700 Q47 V39
Products:
GMAT 1: 700 Q47 V39
Posts: 492
Kudos: 1,217
 [1]
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
try to get the LHS in the way RHS is written. we know that we need power of 2 in the denominator. so lets try to write 20 (numerator) as a sum of powers of two. note: we write as sums so that we can split the two terms and show them as the RHS

\(\frac{4+16}{2^5}\)

\(\frac{2^{2} + 2^{4}}{2^{5}}\)

\(\frac{2^2}{2^5}+\frac{2^4}{2^5}\)

\(\frac{1}{2^3}+ \frac{1}{2^1}\)
3*1=3
User avatar
Jsound996
User avatar
Current Student
Joined: 19 Jan 2018
Last visit: 11 Sep 2023
Posts: 104
Own Kudos:
123
 [1]
Given Kudos: 3,158
Products:
Posts: 104
Kudos: 123
 [1]
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Pdirienzo
If \(\frac{20}{2^{5}} = \frac{1}{2^{m}} + \frac{1}{2^{n}}\) what is nm ?

a) 0
b) 3
c) 8
d) 16
e) 24


We can reduce the left-hand side to \(\frac{5}{2^3}\) = \(\frac{1}{2^m}\) + \(\frac{1}{2^n}\)

We can convert the right-hand side of the formula to \(\frac{2^m + 2^n}{2^(mn)}\)

Look at the denominators only. MN has to equal 3

The answer is B
User avatar
JoeSal
Joined: 23 Oct 2022
Last visit: 30 Apr 2025
Posts: 14
Own Kudos:
Given Kudos: 9
Location: Philippines
Concentration: Technology, Strategy
GMAT Focus 1: 585 Q81 V79 DI77
GPA: 3.19
WE:Account Management (Technology)
GMAT Focus 1: 585 Q81 V79 DI77
Posts: 14
Kudos: 9
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Hi, wanted to ask how you derived the answer from the second statement. My solutions is similar, but I cannot seem to arrive at the answer.
Jsound996
Pdirienzo
If \(\frac{20}{2^{5}} = \frac{1}{2^{m}} + \frac{1}{2^{n}}\) what is nm ?

a) 0
b) 3
c) 8
d) 16
e) 24


We can reduce the left-hand side to \(\frac{5}{2^3}\) = \(\frac{1}{2^m}\) + \(\frac{1}{2^n}\)

We can convert the right-hand side of the formula to \(\frac{2^m + 2^n}{2^(mn)}\)

Look at the denominators only. MN has to equal 3

The answer is B
User avatar
Deepthi13
Joined: 06 May 2025
Last visit: 11 Jul 2025
Posts: 5
Given Kudos: 16
Posts: 5
Kudos: 0
Kudos
Add Kudos
Bookmarks
Bookmark this Post
how did 5 by 2 ^3 come

iPrasad
\(\frac{20}{2^5} = \frac{1}{2^m} + \frac{1}{2^n}\)

\(\frac{5}{2^3} = \frac{1}{2^m} + \frac{1}{2^n}\)

\(\frac{(4 +1)}{2^3} = \frac{1}{2^m} + \frac{1}{2^n}\)

\(\frac{(2^2+1)}{2^3} = \frac{1}{2^m} + \frac{1}{2^n}\)

\(\frac{1}{2^1} + \frac{1}{2^3} = \frac{1}{2^m} + \frac{1}{2^n}\)

this implies m = 1 when n = 3 or m = 3 when n = 1

thus mn = 3
User avatar
Deepthi13
Joined: 06 May 2025
Last visit: 11 Jul 2025
Posts: 5
Given Kudos: 16
Posts: 5
Kudos: 0
Kudos
Add Kudos
Bookmarks
Bookmark this Post
how did 5 by 2 ^3 come

iPrasad
\(\frac{20}{2^5} = \frac{1}{2^m} + \frac{1}{2^n}\)

\(\frac{5}{2^3} = \frac{1}{2^m} + \frac{1}{2^n}\)

\(\frac{(4 +1)}{2^3} = \frac{1}{2^m} + \frac{1}{2^n}\)

\(\frac{(2^2+1)}{2^3} = \frac{1}{2^m} + \frac{1}{2^n}\)

\(\frac{1}{2^1} + \frac{1}{2^3} = \frac{1}{2^m} + \frac{1}{2^n}\)

this implies m = 1 when n = 3 or m = 3 when n = 1

thus mn = 3
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 11 Jul 2025
Posts: 102,634
Own Kudos:
Given Kudos: 98,170
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 102,634
Kudos: 740,476
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Deepthi13
how did 5 by 2 ^3 come

iPrasad
\(\frac{20}{2^5} = \frac{1}{2^m} + \frac{1}{2^n}\)

\(\frac{5}{2^3} = \frac{1}{2^m} + \frac{1}{2^n}\)

\(\frac{(4 +1)}{2^3} = \frac{1}{2^m} + \frac{1}{2^n}\)

\(\frac{(2^2+1)}{2^3} = \frac{1}{2^m} + \frac{1}{2^n}\)

\(\frac{1}{2^1} + \frac{1}{2^3} = \frac{1}{2^m} + \frac{1}{2^n}\)

this implies m = 1 when n = 3 or m = 3 when n = 1

thus mn = 3

\(\frac{20}{2^5}=\\
\\
= \frac{2^2*5}{2^5}=\\
\\
= \frac{5}{2^3}\)
User avatar
sandyphamm
Joined: 13 Jun 2024
Last visit: 11 Jul 2025
Posts: 1
Given Kudos: 79
Products:
Posts: 1
Kudos: 0
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Consider m as the bigger number
\(\frac{5}{2^3} = \frac{1+2^{m-n}}{2^m}\)
--> m=3 and m-n = 2 --> n = 1
mn = 3
Pdirienzo
If \(\frac{20}{2^{5} } = \frac{1}{2^m} + \frac{1}{2^n} \) what is nm ?

(A) 0
(B) 3
(C) 8
(D) 16
(E) 24
Moderators:
Math Expert
102634 posts
PS Forum Moderator
688 posts