Question

How many two-digit integers from 20 to 40 is the ones digit greaterthan the tens digit?

Answer 1

hello

let's write out all the numbers from 20 - 40

$20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40$

what we need to find out here is basically all the numbers having unit digit (ones) from 3 upwards for the 20's and 4 upwards for the 30's

if we count carefully, we have 13 numbers in there that the units (ones) are greater than the tens digit