Saturday

April 18, 2015

April 18, 2015

Posted by **Melissa** on Wednesday, October 7, 2009 at 7:20pm.

I need help.. how do I work this? Step by step please.

- 7th grade math -
**jim**, Wednesday, October 7, 2009 at 8:23pmThe counting principle is oddly-named, since it mostly involves multiplying :-)

It just means that if you can do the first thing x ways, and then in the next step you can do that y ways, then overall you can do the whole thing in x * y ways.

Consider a two-digit PIN.

How many ways can you choose the first digit? 0 through 9 is ten digits, so that's 10 ways.

Choosing the second digit is the same. You can still choose any digit, including the one you picked for the first digit. This makes your second choice _independent_ of your first choice. Your first choice doesn't influence your second. So that's 10 ways.

So the counting principle says that you can choose a 2-digit PIN in 10 * 10 ways.

Move on to the third digit. Um, 10 ways again! This is getting familiar.

And the fourth?

So your answer is?

And as a sanity check, consider that the PIN you must have chosen is an integer between or including 0000 through 9999. How many numbers is that?

**Answer this Question**

**Related Questions**

Mathematics - I have three questions... Okay think of a 1-9 multiplication table...

Calculus - A farmer wishes to enclose a long rectangular pin that will then be ...

MATH - i need help filling this out! 4x-10=32-3x 4x-10+____=32-3x+22 ____-10+...

7th grade math - How would you solve the problem below using subsitution method...

chemistry - What is the percent ionization of a 1.38 mol/L weak acid if its Ka...

Physics - Can someone please show me step by step how to normalize e^-5x in the ...

Algebra help - f(x)=x^3-4x^2-x+4 How do I find the x-intercept for this? This is...

Math - Use multiplication, division, addition and subtraction and at least one ...

math - How many 5-digit bank security Personal Identification Numbers (PIN) ...

math - My problem I have involves a method that requires using the quadratic ...