# How to use mod

#### ver_mathstats

1. The problem statement, all variables and given/known data
Days of the week are 0 - Sun to 6 - Sat. Today is Monday, use addition modulo 7 to find the day of the week 30 days from now.

2. Relevant equations

3. The attempt at a solution
0 - Sunday, 1 - Monday, 2 - Tuesday, 3 - Wednesday, 4 - Thursday, 5 - Friday, and 6 - Saturday. Do we just take 30 mod 7 which is equal to 2 and Tuesday would be our day? Or must I add 1 + 2 = 3 so that Wednesday is the day?

Thank you.

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#### fresh_42

Mentor
2018 Award
1. The problem statement, all variables and given/known data
Number the days of the week from 0 - Sun to 6 - Sat. Today is Monday, use addition modulo 7 to find the day of the week 30 days from now.

2. Relevant equations

3. The attempt at a solution
0 - Sunday, 1 - Monday, 2 - Tuesday, 3 - Wednesday, 4 - Thursday, 5 - Friday, and 6 - Saturday. Do we just take 30 mod 7 which is equal to 2 and Tuesday would be our day? Or must I add 1 + 2 = 3 so that Wednesday is the day?

Thank you.

If today is Monday, then we have day 1. In 30 days we have day 31, which is 3 modulo seven, i.e. Wednesday.
However, if "from now on" means to count today as well, then it's 1+29=30 = 2, Tuesday.

Thus it is more a matter of language than of mathematics. I hate those questions for their notorious ambiguity.

#### ver_mathstats

If today is Monday, then we have day 1. In 30 days we have day 31, which is 3 modulo seven, i.e. Wednesday.
However, if "from now on" means to count today as well, then it's 1+29=30 = 2, Tuesday.

Thus it is more a matter of language than of mathematics. I hate those questions for their notorious ambiguity.
Yes that's why I'm confused, that's how the question was worded and I wasn't sure if I had to include the Monday or not, when I counted it I got Tuesday but I am still unsure if I must include the Monday. Thank you for the reply however.

#### phinds

Gold Member
Yes that's why I'm confused, that's how the question was worded and I wasn't sure if I had to include the Monday or not, when I counted it I got Tuesday but I am still unsure if I must include the Monday. Thank you for the reply however.
If today is Monday, what day is it one day from now? Did you count Monday? If you did, it would still be Monday one day from now.

"How to use mod"

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