Only Two is Allowed

How many 2 digit positive integers are there?

Details and assumptions

The number 12 = 012 12 = 012 is a 2 digit number, not a 3 digit number.


The answer is 90.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

17 solutions

Ayon Pal
Oct 23, 2013

Two digit positive integers are from 10 \boxed{10} up to 99 99 .

So, There is 99 10 + 1 90 99 - 10 + 1 \implies 90 integer.

The last 1 1 is the integer 10 \boxed{10} which we don't count when calculate.

A. R
Oct 21, 2013

There are 9 9 possibilities for the first digit, and 10 10 for the second digit. So there are 90 90 total possibilities.

two digit positive integers are only between 1 to 100, there are 100 digits, just substract the digits which are not two digits like 1-10 and 100 then, 100 - 9+1 = 90

Darryl Yeo
Oct 21, 2013

The lowest positive integer is 10, and the greatest is 99. We can find the number of two-digit numbers by subtracting the two numbers:

99 10 = 89 99-10=89

But we need to make sure we include both 10 and 99. We only included one of them. So we have to add one back.

89 + 1 = 90 89+1=90

There are 90 \boxed{90} two-digit numbers.

2-digit positive integers go from 10 to 99. Counting every integer in this list shows us that there are ( 99 10 ) + 1 = 90 (99 - 10) + 1 = \text{90} 2-digit positive integers.

Mohith Manohara
Oct 20, 2013

1(0-10_ =10 nos.

there are 9 possible tens digit numbers.

9 × 10 = 90 9\times10=\boxed{90}

Cee Jhay Castro
Aug 12, 2013

it starts from 10, 11, 12, 13, 14, ... ,97, 98,99 ....

Moderator note:

This isn't a complete explanation. It is not immediately obvious what is being done.

You should ensure that your explanations are clear enough that those who are unable to solve the problem can understand how you worked through it.

it doesn't work

Har Chun Wai - 7 years, 10 months ago
Habibah Auni
Mar 4, 2014

the first two digit is = 10. The first number is referred to "a".It followed by 11,12,13,... So,the "b"(ratio) is 1.And the "Un" is 99 ( because it is the last two digits,and we want to find "n"). Do it with formula will be = Un=a+(n-1)b 99=10+(n-1)1 99=10+n-1 99=9+n n=99-9=90.

Lakshmi Tumati
Jan 4, 2014

There are 90 positive 2 digit integers. The 2 digit positive integers range from 10-99, which are 90 different numbers.

Marcos Oliveira
Jan 3, 2014
  • 99 -10 = 89 -----> 89 + 1 = 90 \boxed{90}
Judhistira Junior
Oct 26, 2013

99-9=90 the nine number are (1 to 9)

Kelvin Ng
Oct 26, 2013

99-10+1=90

Daniel Ferreira
Oct 25, 2013

9 10 = 90 9 \cdot 10 = \\ \boxed{90}

Samrit Pramanik
Oct 24, 2013

In 1 to 99, there are 99 positive integer. Among them 1 to 9, there are 1 digit. So, the required answer is (99-9) = \boxed{90}

Test User
Oct 22, 2013

The two digit numbers are all in the range [10, 99]. If you subtract 9 from each element in this list, you get the range [1, 90] which (if you look at it: 1, 2, 3...) has a length of 90. Therefore, there are 90 2-digit positive integers.

Priyansh Sangule
Oct 21, 2013

We can say that - we have * 9 possibilities * for the * tens digit * {excluding the "zero"}

and 10 possibilities for the unit digit .

9 × 10 = 90 \boxed{9} \times \boxed{10} = 90

Hence there are 90 such numbers .

Icon Lacanaria
Aug 16, 2013

Integers are whole numbers (including zero) and their negatives. I = {..., -2, -1, 0, 1, 2, ...} The positive integers are restricted to just: P = {1, 2, 3, ...} The two digit numbers in this set begin at 10 and end at 99. To count them, simply subtract and add one: 99 - 10 + 1 = 90. Or, count starting at 11 and you'll end up with 89, then add one more for 10 to get 90.

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...