Question

how many integers between 999 and 9999 either begin or end with 3​

Answer 1

Answer:

1900 integers

Step-by-step explanation:

The answer is there are 1900 integers between 999 & 9999 that begin or end with a three.

Answer 2

Answer:

$1800$ integers between $999$ and $9999$ begin or end with $3.$

Step-by-step explanation:

Let $A:$ The set of intergers between $999$ and $9999$ begin with $3.$

Let $B:$ The set of intergers between $999$ and $9999$ end with $3.$

      $A=1*10^3($begin with $3=9:1,9:10,9:10,9:10)$

      $B=9*10*10*1($end with $3=9:9,9:10,9:10,9:1)$

    $AB=1*10^2*1($begin and end with $3=9:1,9:10,9:10,9:1)$

$A$∪$B=A+B-A$∩$B$

        $=10^3+900-100$

        $=1000+900-100$

        $=1800$