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Re: How many different two-digit positive integers are there [#permalink]
22 Feb 2018, 17:39

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answer: D integers are positive and two digits like 17, 68, 97, etc. in the two digits positive integers tens digit is the one with power 1, in the 17: tens digit is 1. In the 68: tens digit is 6. The question wants numbers which their tens digit is more than 6, Thus their tens digit can be 7, 8 and 9. Units digit is the digit with power 0, in 17: unit digit is 7, in 68: unit digit is 8. Unit digit must be less than 4, So it can be 0, 1, 2, 3. So we can have 7,8,9 in the tens digit and 0,1,2,3 in the unit digit. Possible numbers are: 70, 71, 72, 73 80, 81, 82, 83 90, 91, 92, 93 there are 12 numbers with these circumstances. *unit digit is the digit with power 0, tens digit is the digit with power 1, etc.
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can you please tell, when should one look at the option choices, I avoid looking at them before I derive the solution myself, often it is wrong and at the testing conditions it makes me panic when I see that my answer is not the listed one.. in such case I pick the one which is closest to mine answer..which is more often wrong approach..

when should I consider OPTION CHOICES in order to derive the at the solution ... can you also share a link to GRE MATHS STRATEGIES.

How many different two-digit positive integers are there in which the tens digit is greater than 6 and the units digit is less than 4 ?

A) 7

B) 9

C) 10

D) 12

E) 24

If the tens digit is greater than 6, there are 3 options (7, 8, 9) for the tens digit. If the units digit is less than 4, there are 4 options (3, 2, 1, 0) for the units digit, so we have a total of 3 x 4 = 12 ways to create the number.

Re: How many different two-digit positive integers are there in [#permalink]
22 Jan 2019, 06:39

1

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Expert's post

IshanGre wrote:

can you please tell, when should one look at the option choices, I avoid looking at them before I derive the solution myself, often it is wrong and at the testing conditions it makes me panic when I see that my answer is not the listed one.. in such case I pick the one which is closest to mine answer..which is more often wrong approach..

when should I consider OPTION CHOICES in order to derive the at the solution ... can you also share a link to GRE MATHS STRATEGIES.

Thanks in advance.

You should ALWAYS check the answer choices BEFORE performing any calculations. There are many reasons for this (see video below), but here's a rudimentary example:

Let's say you have a counting question, and you recognize that the answer will equal 26^3 Let's also say the answer choices are: A) 17,572 B) 17,573 C) 17,574 D) 17,575 E) 17,576

If we try head straight to the online calculator (or start multiplying 26x26x26 on scratch paper), we're missing out on a 1-second answer.

Since all powers of 26 will have 6 as a units digit, we know that the correct answer is E

For more on this, watch:

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Re: How many different two-digit positive integers are there in [#permalink]
02 Feb 2019, 00:59

I have a big question regarding the concept of this question. I am looking at some questions involving integers that are not considering 0 as a positive integer. Here is an example from Barrons Model paper test 2:

Q. A number x is chosen at random from the set of integers less than 10. What is the probability that 9/x > x?

I considered 0 as a positive integer and got 3/10. But the explanation does not consider 0 and the correct answer is 2/9.