gmat prep1 q's. please help!

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karenmeow: Junior | Next Rank: 30 Posts; Posts: 12; Joined: Fri Jun 27, 2008 3:29 pm

by karenmeow » Fri Jul 11, 2008 2:55 pm

please help me with these questions... i dont know how to get the answer!

1. pump a, b, & c operate at constant rates. pump a & b, simultaneously, fill a tank in 6/5 hr; pump a & c, simultaneously, fill a tank in 3/2 hr; pump b & c, simultaneously, fill a tank in 2 hrs. how many hrs does it take a, b, & c, simultaneously, to fill a tank?

answer: 1 hr

2. if each term in sum a1+a2+...+an is either 7 or 77, and the sum equals 350, which can be n?
choices: 38, 39, 40, 41, 42

answer: 40

3. alice's take home pay is the same each month. she saves same fraction each month. the total amt she saved at the end of the year was 3 times the amt of the portion she did NOT save. if all the money she saved last yr was from her pay, what fraction of her pay did she save each month?

answer: 1/5

4. the perimeter of an isosceles right triangle is 16+16(sq rt 2). what is the length of the hypotenuse?

answer: 16

5. 3 grades of milk are 1%, 2%, 3% fat. if x gallons of 1%, y gallons of 2%, and z gallons of 3% are mixed to give x+y+z gallons a 1.5% grade, what is x in terms of y & z?

answer: y+3z

thanks!

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Source: Beat The GMAT — Problem Solving | Fri Jul 11, 2008 2:55 pm

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lunarpower: GMAT Instructor; Posts: 3380; Joined: Mon Mar 03, 2008 1:20 amFollowed by: 1535 members; Thanked: 2256 times; GMAT Score:800

by lunarpower » Fri Jul 11, 2008 8:57 pm

please post problems in separate threads.

i have performed this separation for these problems as a courtesy (to you and, more importantly, to the thousands of other users who prefer 1 problem per post); if you post problems in the future, please create a separate thread for each problem.
thank you.

the first problem may be found at
https://www.beatthegmat.com/pump-a-b-c-o ... html#57014

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lunarpower: GMAT Instructor; Posts: 3380; Joined: Mon Mar 03, 2008 1:20 amFollowed by: 1535 members; Thanked: 2256 times; GMAT Score:800

by lunarpower » Sat Jul 12, 2008 1:51 am

third problem
https://www.beatthegmat.com/alice-s-take ... html#57071

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lunarpower: GMAT Instructor; Posts: 3380; Joined: Mon Mar 03, 2008 1:20 amFollowed by: 1535 members; Thanked: 2256 times; GMAT Score:800

by lunarpower » Sat Jul 12, 2008 1:52 am

second problem
https://www.beatthegmat.com/if-each-term ... 13856.html

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lunarpower: GMAT Instructor; Posts: 3380; Joined: Mon Mar 03, 2008 1:20 amFollowed by: 1535 members; Thanked: 2256 times; GMAT Score:800

by lunarpower » Sat Jul 12, 2008 1:53 am

4th problem (from another forum)

https://www.manhattangmat.com/forums/iso ... t2694.html

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antyagi: Junior | Next Rank: 30 Posts; Posts: 12; Joined: Thu Apr 24, 2008 3:11 pm; Location: Toronto

by antyagi » Sat Jul 12, 2008 4:40 am

In the 3rd problem, where does the problem states that the
"the total amt she saved at the end of the year was 3 times the amt of the portion she did NOT save" is applicable for a year.
i.e instead of 12x = 3(x-y) why it cannot be x = 3(x-y) ??

Thanks,
Ankur Tyagi

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vivekverma: Newbie | Next Rank: 10 Posts; Posts: 5; Joined: Wed Jan 23, 2008 11:38 am

by vivekverma » Sat Jul 12, 2008 7:30 am

Solutions :

1. 1/a+1/b = 5/6
1/a+1/c = 2/3
1/b+1/c = 1/2

2(1/a+1/b+1/c)=5/6+2/3+1/2
=> 1/a+1/b+1/c = 1

2. Out of n numbers, let no. of 77's be x :
So, we have sum = 77x + 7(n-x) = 350
=> n+10x = 50
For different values of x : if x=1 n=40(Ans.)

3. For isosceles triangle, sides = x,x,x(root 2)
Sum of all sides = perimeter = 2x+x(root 2) = 16+16(root 2)
=> 16(1+root2) = (root2)x(1+root2)
=> x(root 2) = 16 (Ans.)

4. Total Pay = P
Saving = S
12 month saving = 12*S = 3(P-S)
=> S/P = 1/5

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hakyology: Senior | Next Rank: 100 Posts; Posts: 66; Joined: Tue Jun 05, 2007 1:39 pm; Thanked: 1 times

5. y+3z

by hakyology » Sat Jul 12, 2008 1:14 pm

0.01x + 0.02y + 0.03z = 0.015(x + y + z )

then u will get y+3z.

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lunarpower: GMAT Instructor; Posts: 3380; Joined: Mon Mar 03, 2008 1:20 amFollowed by: 1535 members; Thanked: 2256 times; GMAT Score:800

by lunarpower » Sat Jul 12, 2008 3:42 pm

antyagi wrote:In the 3rd problem, where does the problem states that the
"the total amt she saved at the end of the year was 3 times the amt of the portion she did NOT save" is applicable for a year.
i.e instead of 12x = 3(x-y) why it cannot be x = 3(x-y) ??

the original poster left out the rather important word "monthly" in the original problem statement.

go to the separate thread i created for that problem; i've posted the correction there.

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