document.write( "Question 1150894: We call a number a descending number if each digit is strictly smaller than the digit that comes before it. For example, 863 is a descending number. How many 3-digit descending numbers are there? \n" ); document.write( "
Algebra.Com's Answer #772464 by jim_thompson5910(35256)![]() ![]() ![]() You can put this solution on YOUR website! \n" ); document.write( "If 2 is in the hundreds place, then there is only 1 three-digit number that is a descending number and it is 210.\r \n" ); document.write( " \n" ); document.write( "\n" ); document.write( "If 3 is in the hundreds place, then there are three such descending numbers \n" ); document.write( "310 \n" ); document.write( "320 \n" ); document.write( "321\r \n" ); document.write( " \n" ); document.write( "\n" ); document.write( "If 4 is in the hundreds place, then we have six descending numbers \n" ); document.write( "410 \n" ); document.write( "420 \n" ); document.write( "421 \n" ); document.write( "430 \n" ); document.write( "431 \n" ); document.write( "432\r \n" ); document.write( " \n" ); document.write( " \n" ); document.write( "\n" ); document.write( "If 5 is in the hundreds place, then we have ten descending numbers \n" ); document.write( "510 \n" ); document.write( "520 \n" ); document.write( "521 \n" ); document.write( "530 \n" ); document.write( "531 \n" ); document.write( "532 \n" ); document.write( "540 \n" ); document.write( "541 \n" ); document.write( "542 \n" ); document.write( "543\r \n" ); document.write( " \n" ); document.write( "\n" ); document.write( "The counts so far are: 1, 3, 6, 10\r \n" ); document.write( " \n" ); document.write( "\n" ); document.write( "The jump from 1 to 3 is +2 \n" ); document.write( "The jump from 3 to 6 is +3 \n" ); document.write( "The jump from 6 to 10 is +4\r \n" ); document.write( " \n" ); document.write( "\n" ); document.write( "This pattern continues because we have 15 descending numbers if 6 is the hundreds digit \n" ); document.write( "610 \n" ); document.write( "620 \n" ); document.write( "621 \n" ); document.write( "630 \n" ); document.write( "631 \n" ); document.write( "632 \n" ); document.write( "640 \n" ); document.write( "641 \n" ); document.write( "642 \n" ); document.write( "643 \n" ); document.write( "650 \n" ); document.write( "651 \n" ); document.write( "652 \n" ); document.write( "653 \n" ); document.write( "654\r \n" ); document.write( " \n" ); document.write( "\n" ); document.write( "And there are 15+6 = 21 descending numbers with 7 as the hundreds digit, 21+7 = 28 descending numbers with 8 as the hundreds digit, and finally 28+8 = 36 descending numbers with 9 as the hundreds digit.\r \n" ); document.write( " \n" ); document.write( "\n" ); document.write( "The counts are \n" ); document.write( "1,3,6,10,15,21,28,36 \n" ); document.write( "Add them up \n" ); document.write( "1+3+6+10+15+21+28+36 = 120\r \n" ); document.write( " \n" ); document.write( "\n" ); document.write( "Answer: 120\r \n" ); document.write( " \n" ); document.write( "\n" ); document.write( "Below is a pastebin link of all 120 three-digit descending numbers \n" ); document.write( "https://pastebin.com/WqFYtfc4 \n" ); document.write( "This is to avoid adding further clutter to this current page. \n" ); document.write( " \n" ); document.write( " |