Math Help - algorithm

1. algorithm

PROJECT: CREATING AN ALGORITHM

Imagine working with a younger sibling or student who is having trouble multiplying by 9s. Create an algorithm to help the student learn how to do this easily. Then notate whether the given algorithm is equivalent or not. You may need to use outside resources to help you.
Hint: 10 - 1 = 9
Describe your algorithm in the space provided below.

2. Originally Posted by manznitaa5
PROJECT: CREATING AN ALGORITHM

Imagine working with a younger sibling or student who is having trouble multiplying by 9s. Create an algorithm to help the student learn how to do this easily. Then notate whether the given algorithm is equivalent or not. You may need to use outside resources to help you.
Hint: 10 - 1 = 9
Describe your algorithm in the space provided below.
Do you mean something like this(?):

Let $1 \leq a \leq 10$

Then the result of $a \cdot 9$ is a 2-digit-number whose

first digit is $a-1$ and it's

second digit is $9-first\ digit$

Example: $5 \cdot 9$

first digit: $5-1=\boxed{4}$
second digit: $9-4=\boxed{5}$

and therefore the result is 45

3. Originally Posted by manznitaa5
PROJECT: CREATING AN ALGORITHM

Imagine working with a younger sibling or student who is having trouble multiplying by 9s. Create an algorithm to help the student learn how to do this easily. Then notate whether the given algorithm is equivalent or not. You may need to use outside resources to help you.
Hint: 10 - 1 = 9
Describe your algorithm in the space provided below.
Multiply by 10 by adding a 0 to the left end of the string of digits representing the number, then suntract the original number from this new number.

RonL