solutions to combinatorics exercises

Your answer is wrong (to the problem of, how many 2-digit numbers have the digit of tens strictly smaller than the digit of units)

Note by Predrag Tosic
3 years, 7 months ago

MarkdownAppears as
*italics* or _italics_ italics
**bold** or __bold__ bold
- bulleted- list
• bulleted
• list
1. numbered2. list
1. numbered
2. list
Note: you must add a full line of space before and after lists for them to show up correctly
paragraph 1paragraph 2

paragraph 1

paragraph 2

[example link](https://brilliant.org)example link
> This is a quote
This is a quote
    # I indented these lines
# 4 spaces, and now they show
# up as a code block.

print "hello world"
# I indented these lines
# 4 spaces, and now they show
# up as a code block.

print "hello world"
MathAppears as
Remember to wrap math in $$...$$ or $...$ to ensure proper formatting.
2 \times 3 $$2 \times 3$$
2^{34} $$2^{34}$$
a_{i-1} $$a_{i-1}$$
\frac{2}{3} $$\frac{2}{3}$$
\sqrt{2} $$\sqrt{2}$$
\sum_{i=1}^3 $$\sum_{i=1}^3$$
\sin \theta $$\sin \theta$$
\boxed{123} $$\boxed{123}$$

Sort by:

Yes, you are correct. 'My' question has the answer of 36, your question has the answer of 45. My recollection of the exact formulation was wrong (generally I work on these problems in my head, i.e.., without paper, pen or repeated looking on the screen -- so, it's probably bound to happen every now and then...)

- 3 years, 7 months ago

Do you have any feedback on your usage of Brilliant? Is there any thing that you would like us to improve on?

Staff - 3 years, 7 months ago

If you believe that a practice problem is wrong, you can report it directly and we will take a look at it.

I do not see a question of "how many 2-digit numbers have the digit of tens strictly smaller than the digit of units" in the practice section. The closest question that I see is "How many 2 digit numbers are there, such that the units digit is strictly smaller than the tens digit?". These 2 questions would have different answers.

Staff - 3 years, 7 months ago