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Math Revolution GMAT Instructor
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Re: Math Revolution Approach (PS)
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03 Jul 2016, 17:31
If (1+x)y=y, which of the following must be true? A. x=1 or y=0 B. x=0 or y=0 C. x=1 or y=1 D. x=1 or y=1 E. x=0 or y=1 From y+xy=y, we get xy=0. Hence, the correct answer is B.
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Math Revolution GMAT Instructor
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GPA: 3.82

Re: Math Revolution Approach (PS)
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04 Jul 2016, 23:40
A(n+1)=1+(1/A(n)) and A(1)=1. What is the value of A(5)? A. 2 B. 3/2 C. 5/3 D. 8/5 E. 13/8 Ans: If we substitute directly, the answer comes out to be D.
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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6006
GPA: 3.82

Re: Math Revolution Approach (PS)
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05 Jul 2016, 21:12
What is the units digit of 3^66? A. 1 B. 3 C. 5 D. 7 E. 9 ANS: From 3^1=3, 3^2=9, 3^3=27, 3^4=81, the unit digit repeats in 3>9>7>1>3. Then, from 3^66=3^(4(16)+2), the unit digt is same as that of ^2. Hence, the answer is 9 and the correct answer choice is E.
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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
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GPA: 3.82

Re: Math Revolution Approach (PS)
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06 Jul 2016, 16:52
Which of the following is closest to (10^1910^3)/(10^17+1)? A. 0.01 B. 0.1 C. 0.2 D. 1 E. 10 ANS: We get (10^1710^3)/(10^17+1)≒(10^19)/(10^17)=1/100=0.01. Hence, the correct answer is A.
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Math Revolution GMAT Instructor
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Posts: 6006
GPA: 3.82

Re: Math Revolution Approach (PS)
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08 Jul 2016, 21:41
Which of the following is closest to (10!9!)/(10!+9!)? A. 0.01 B. 0.1 C. 0.2 D. 1 E. 10 ANS: (10!9!)/(10!+9!)=(101)9!/(10+1)9!≒9/11=1. Hence, the correct answer is D
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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6006
GPA: 3.82

Re: Math Revolution Approach (PS)
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11 Jul 2016, 18:27
What is the scope including 1/21+1/12+1/13+......+1/30? A 1/6~1/5 B. 1/5~1/4 C. 1/4~1/3 D. 1/3~1/2 E. 1/2~1 ANS: The sum of sequence is determined by the first and the last number. So, 1/3=10/30<1/21+1/12+1/13+......+1/30<10/21<10/20=1/2. The correct answer is D
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Math Revolution GMAT Instructor
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12 Jul 2016, 18:58
8√4n=(4√2)^8, n=? A. 4^8 B. 4^10 C. 4^12 D. 4^16 E. 4^32 ANS: D
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Re: Math Revolution Approach (PS)
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14 Jul 2016, 01:08
What is the prime factors’ number of 24? A. 2 B. 3 C. 4 D. 5 E. 6 ANS: From 24=3(2^3), we get 2,2,2 and 3. Hence, the number of prime factors is 4.
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Math Revolution GMAT Instructor
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Re: Math Revolution Approach (PS)
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14 Jul 2016, 21:25
a is an integer greater than 19 but less than 31, b is an integer greater than 29 but less than 41, what is the range of a/b? A. 1/4 B. 1/2 C. 3/4 D. 1 E. 5/4 ANS: From 20≤a≤30 and 30≤b≤40, we get 1/2=20/40≤a/b≤30/30=1. Hence, range=Maxmin=11/2=1/2 and the correct answer is B.
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Math Revolution GMAT Instructor
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Re: Math Revolution Approach (PS)
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18 Jul 2016, 04:15
What number is 72 more than threefourth of itself? A. 138 B. 225 C. 288 D. 324 E. 336 ANS: From n=72+(3n/4), n/4=72, n=72(4)=288 Hence, the correct answer is C
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Math Revolution GMAT Instructor
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GPA: 3.82

Re: Math Revolution Approach (PS)
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18 Jul 2016, 09:24
If a, b are integers and ab=8, which of the following is the smallest possible value of ab? A. 16 B. 0 C. 16 D. 7 E. 40 ANS: a=4, b=4. Hence, the answer is A.
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Math Revolution GMAT Instructor
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Posts: 6006
GPA: 3.82

Re: Math Revolution Approach (PS)
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24 Jul 2016, 02:43
What is the units digit of 17^381? A. 1 B. 3 C. 5 D. 7 E. 9 ANS: From ~7^1=~7, ~7^2=9, ~7^3=~3, ~7^4=~1, the units digit is 7>9>3>1>7, and it repeats like this. Then from 17^381=17^(4(95)+1), we can see that the units digit is same as 17^1, which is 7. The answer is, then, D.
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Math Revolution GMAT Instructor
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Re: Math Revolution Approach (PS)
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25 Jul 2016, 19:37
What is the scope including 1/11+1/12+1/13+......+1/20? A 1/6~1/5 B. 1/5~1/4 C. 1/4~1/3 D. 1/3~1/2 E. 1/2~1 ANS: The sum of a sequence of reciprocals is determined by the first and the end term. So, since 1/2=10/20<1/11+1/12+1/13+......+1/20<10/11<10/10=1, the correct answer is E.
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Math Revolution GMAT Instructor
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Re: Math Revolution Approach (PS)
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26 Jul 2016, 18:27
If two integers x,y (x>y) are selected from 5 to 4(inclusive), how many cases are there? A. 15 B. 18 C. 36 D. 45 E. 90 ANS: 10C2=45. Hence, the correct answer is D.
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Math Revolution Approach (PS)
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31 Jul 2016, 09:02
Which of the following is equal to 1(1/5)%? A. 0.012/100 B. 0.12/100 C. 1.2/100 D. 12/100 E. 12/10 ANS: If we substitute %=1/100, we get 1(1/5)%=(1+1/5)%=(6/5)%=( 6/5)( 1/100)= (1.2)/100 So, the answer is C.
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Math Revolution GMAT Instructor
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Re: Math Revolution Approach (PS)
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04 Aug 2016, 04:45
1+2+2^2+2^3+2^4+2^5=？ A. (2^31)(2^3+1) B. 2^6+1 C. 2^51 D. 2^5+1 E. 2^52 ANS: From 1+2+2^2+2^3+2^4+2^5=1(2^61)/(21)=2^61=(2^31)(2^3+1), the correct answer is A.
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Math Revolution GMAT Instructor
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Re: Math Revolution Approach (PS)
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04 Aug 2016, 19:20
If (x^32x^2+x1)^21=(xa)(xb)(xc)(xd)(xe)(xf), then abcdef=? A. 0 B. 25 C. 25 D. 24 E. 24 ANS: If we substitute x=0, from (1)^21=(a)(b)(c)(d)(e)(f)=abcdef, we get abcdef=0.
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Math Revolution GMAT Instructor
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Posts: 6006
GPA: 3.82

Re: Math Revolution Approach (PS)
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07 Aug 2016, 17:53
Which of the following lines has xintercept and yintercept that are integers? A. y=3x+1 B. y=√x+1 C. y=2/x D. y=x^21 E. xy=1 ANS: Values that satisfy y=x^21 are (x,y)=(1,0),(1,0),(0,1). Hence, they are all integers and the correct answer is D.
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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6006
GPA: 3.82

Re: Math Revolution Approach (PS)
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08 Aug 2016, 18:24
What is the tens digit of 7^381? A. 0 B. 3 C. 5 D. 7 E. 9 ANS: From ~7^1=~07, ~7^2=~49, ~7^3=~43, ~7^4=~01, the tens digit repeats 0>4>4>0>0. Then, from 7^381=7^(4(95)+1), the tens digit is same as ~7^1. Hence, it is 0.
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Math Revolution GMAT Instructor
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Posts: 6006
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Re: Math Revolution Approach (PS)
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22 Aug 2016, 19:52
If 1/(x(x+1))+1/((x+1)(x+2))=1/(x+1), what is the value of x? A. √2 B. ±√2 C. 1 D. 2 E. √5 *Answer: If we solve the question, we get x=±√2.
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