Question

The number of two-digit positive integers for which the units digit is not equal to the tens digit.

Answer 1

HI!!

Answer 2

hi misty =)

Answer 3

my guess is \(81\)
reason as follows:
you have nine choices for the tens place digit (it cannot be zero) then another 9 choices for the ones place (it can be zero, but it cannot be the tens digit)

Answer 4

by the counting principle you get \(9\times 9=81\)

Answer 5

ouuuuu niceeeee okay got it thanks!

Answer 6

course i could be wrong
maybe @geerky42 has a different answer

Answer 7

it was right

Answer 8

There are \(99-10+1 = 90\) two digits numbers.

Now exclude numbers where tens digit and unit digit are same;
11, 22, 33, 44, ..., 99
There are \(9\) of them.

So you have \(90-9 = \boxed{81}\)

So @misty1212 is correct.

Answer 9

hey why do u exclude the 11, 22,33,44 etc.?????

Answer 10

for which the units digit is not equal to the tens digit.

Answer 11

but doesnt that just mean 10, 20, 30, 40 etc?

Answer 12

No. "units digit is equal to the tens digit" means 11, 22, 33, etc.

So here, we have "units digit is NOT equal to the tens digit", which means

10, 12, 13, ..., 20, 21, 23, ..., 31, 32, 34, ..., etc.

Answer 13

We counted ALL two digits numbers, then we un-counted number where "units digit is equal to the tens digit"