Six math need to solve

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monirjewel: Newbie | Next Rank: 10 Posts; Posts: 4; Joined: Fri Jan 29, 2010 5:47 am; Location: University of Dhaka, Bangladesh

by monirjewel » Sat Nov 13, 2010 11:18 pm

If x and y are integers, what is the value of 2x^6y-4 ?
(1) X^2y=16
(2) xy=4

The function f is defined for each positive three digit integer n by f(n)=2^x3^y5^z, where x, y and z are hundreds, tens, and units digits of n, respectively. If m and v are three digit positive integers such that f(m)=9 f(v),then m-v=
(A) 8
(B) 9
(C) 18
(D) 20
(E) 80

A rectangular floor that measures 8 meters by 10 meters is to be covered with carpet squares that each measure 2 meters by 2 meters. If carpet squares cost $12 apiece, what is the total cost for the number of carpet squares needed to cover the floor?
(A) $200
(B) $240
(C) $480
(D) $960
(E) $1920

Which of the following is closet to 10^180-10^30?
(A) 10^210
(B) 10^180
(C) 10^150
(D) 10^90
(E) 10^6

If x, y, and z are consecutive even positive integers, which of the following could be equal to x+y+z?
(A) 141
(B) 200
(C) 318
(D) 391
(E) 412

A sum of money was divided between John and Anne such that the ratio of John's share to Anne's share was 5 to 3. If John's share exceeded 5/9 of the sum of money by $50, what was Anne's share?
(A) $180
(B) $270
(C) $340
(D) $450
(E) $720

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Source: Beat The GMAT — Problem Solving | Sat Nov 13, 2010 11:18 pm

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Rahul@gurome: GMAT Instructor; Posts: 1179; Joined: Sun Apr 11, 2010 9:07 pmFollowed by: 88 members; Location: Milpitas, CA; Thanked: 447 times

by Rahul@gurome » Sat Nov 13, 2010 11:54 pm

Question Number 6:

A sum of money was divided between John and Anne such that the ratio of John's share to Anne's share was 5 to 3. If John's share exceeded 5/9 of the sum of money by $50, what was Anne's share?
(A) $180
(B) $270
(C) $340
(D) $450
(E) $720

Assume that the sum of money = $x
John's share = $(5x/8)
Anne's share = $(3x/8)

According to the question,

John's share = (5/9)*(Sum of the money) + $50

Therefore, (5x/8) = (5/9)*(x) + 50
=> x/8 = x/9 + 10
=> (x/8 - x/9) = 10
=> x/72 = 10
=> x = 720
=> (3x/8) = (3/8)*(720) = 270

Thus, Anne's share is $270.

The correct answer is B.

Last edited by Rahul@gurome on Sun Nov 14, 2010 12:01 am, edited 1 time in total.

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by Rahul@gurome » Sun Nov 14, 2010 12:00 am

Question Number 5:

If x, y, and z are consecutive even positive integers, which of the following could be equal to x+y+z?
(A) 141
(B) 200
(C) 318
(D) 391
(E) 412

Say, x = 2n, then, y = (2n + 2) and z = (2n + 4)

Therefore, (x + y + z) = 2n + (2n + 2) + (2n + 4) = (6n + 6) = 6(n + 1)

Thus (x + y + z) must be divisible by 6.
Among the options only 318 is divisible by 6.

The correct answer is C.

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by Rahul@gurome » Sun Nov 14, 2010 12:06 am

Question Number 4:

Which of the following is closet to 10^180-10^30?
(A) 10^210
(B) 10^180
(C) 10^150
(D) 10^90
(E) 10^6

(10^180 - 10^30) = (10^30)*(10^150 - 1) â‰ˆ (10^30)*(10^150) = (10^180)

This is because, (10^150 - 1) â‰ˆ (10^150)

The correct answer is B.

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by Rahul@gurome » Sun Nov 14, 2010 12:11 am

Question Number 3:

A rectangular floor that measures 8 meters by 10 meters is to be covered with carpet squares that each measure 2 meters by 2 meters. If carpet squares cost $12 apiece, what is the total cost for the number of carpet squares needed to cover the floor?
(A) $200
(B) $240
(C) $480
(D) $960
(E) $1920

Area of the rectangular floor = (8*10) sq. meters = 80 sq meters
Area of the square carpets = (2*2) sq. meters = 4 sq. meters

Number of carpets required to cover the floor = (80/4) = 20

Total cost of the carpets = ($12 per carpet)*(20 carpets) = $240

The correct answer is B.

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by Rahul@gurome » Sun Nov 14, 2010 12:21 am

Question Number 2:

The function f is defined for each positive three digit integer n by f(n)=2^x3^y5^z, where x, y and z are hundreds, tens, and units digits of n, respectively. If m and v are three digit positive integers such that f(m)=9 f(v),then m-v=
(A) 8
(B) 9
(C) 18
(D) 20
(E) 80

Say, m = (100A + 10B + C) => A is the hundredths, B is the tenths and C is the units digit of m.
and, v = (100X + 10Y + Z) => X is the hundredths, Y is the tenths and Z is the units digit of v.

Thus, f(m) = (2^A)*(3^B)*(5^C)
and, f(v) = (2^X)*(3^Y)*(5^Z)

Now, f(m) = f(v) => (2^A)*(3^B)*(5^C) = 9*(2^X)*(3^Y)*(5^Z) = (2^X)*(3^(Y + 2))*(5^Z)

Comparing the exponents of 2, 3 and 5,

A = X
B = Y + 2
C = Z

Now, (m - v) = (100A + 10B + C) - (100X + 10Y + Z) = 100*(A - X) + 10*(B - Y) + (C - Z) = 10*2 = 20

The correct answer is D.

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ctur9967: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Mon Sep 27, 2010 9:51 pm; GMAT Score:730

by ctur9967 » Mon Nov 15, 2010 1:31 am

Hi,

Thanks for the tips.

I do not, however, see the link between the hundreds digit, the tens digit and the unit digit and the ability to express them as part of the function.

Ie why does f(100A + 10B + C ) = 2^A*3^B^5^C

Cheers,

Chris

Rahul@gurome wrote:Question Number 2:

The function f is defined for each positive three digit integer n by f(n)=2^x3^y5^z, where x, y and z are hundreds, tens, and units digits of n, respectively. If m and v are three digit positive integers such that f(m)=9 f(v),then m-v=
(A) 8
(B) 9
(C) 18
(D) 20
(E) 80
Say, m = (100A + 10B + C) => A is the hundredths, B is the tenths and C is the units digit of m.
and, v = (100X + 10Y + Z) => X is the hundredths, Y is the tenths and Z is the units digit of v.

Thus, f(m) = (2^A)*(3^B)*(5^C)
and, f(v) = (2^X)*(3^Y)*(5^Z)

Now, f(m) = f(v) => (2^A)*(3^B)*(5^C) = 9*(2^X)*(3^Y)*(5^Z) = (2^X)*(3^(Y + 2))*(5^Z)

Comparing the exponents of 2, 3 and 5,
A = X
B = Y + 2
C = Z
Now, (m - v) = (100A + 10B + C) - (100X + 10Y + Z) = 100*(A - X) + 10*(B - Y) + (C - Z) = 10*2 = 20

The correct answer is D.

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by Rahul@gurome » Mon Nov 15, 2010 1:41 am

ctur9967 wrote:Hi,

Thanks for the tips.

I do not, however, see the link between the hundreds digit, the tens digit and the unit digit and the ability to express them as part of the function.

Ie why does f(100A + 10B + C ) = 2^A*3^B^5^C

Read the question properly. The function is defined in that way.

The function f is defined for each positive three digit integer n by f(n)=2^x3^y5^z, where x, y and z are hundreds, tens, and units digits of n, respectively

Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)

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ctur9967: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Mon Sep 27, 2010 9:51 pm; GMAT Score:730

by ctur9967 » Mon Nov 15, 2010 2:39 am

Thankyou.

I clearly glazed over the question.

keep up the great work

Rahul@gurome wrote:
ctur9967 wrote:Hi,

Thanks for the tips.

I do not, however, see the link between the hundreds digit, the tens digit and the unit digit and the ability to express them as part of the function.

Ie why does f(100A + 10B + C ) = 2^A*3^B^5^C
Read the question properly. The function is defined in that way.

The function f is defined for each positive three digit integer n by f(n)=2^x3^y5^z, where x, y and z are hundreds, tens, and units digits of n, respectively

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