Gift Wrap Combinations
Date: 04/20/99 at 23:12:15 From: Matthew Subject: Multiplying This is the problem. I think I should add but my mom said to multiply. My answer is 5 and my mom's answer is 6. Am I right or is my mom? The problem: Mary is wrapping a gift. She has 3 different colors of ribbon and 2 different colors of wrapping paper. =How many many different ways can she wrap the gift? Thank you.
Date: 04/21/99 at 10:24:05 From: Doctor Rick Subject: Re: Multiplying Hi, Matthew, welcome to Ask Dr. Math! Let's try it. Let's say Mary has: red ribbon green ribbon yellow ribbon striped paper white paper If she picks ONE of these 5 things to wrap the gift, she has 5 ways to do it. But that's not how we usually wrap gifts. (Once my brother built a greenhouse for my father, and he wrapped it with a huge ribbon but no wrapping paper.) Normally, though, we wrap it in paper AND a ribbon. If Mary does it this way, she has these choices: striped paper, red ribbon striped paper, green ribbon striped paper, yellow ribbon white paper, red ribbon white paper, green ribbon white paper, yellow ribbon Well, it looks like your mom is right. She has probably wrapped a lot of presents, so this was easy for her. But why do you multiply? We can write the choices as a table, like this: PAPER: striped white +-------+-------+ RIBBON: red | | | +-------+-------+ green | | | +-------+-------+ yellow | | | +-------+-------+ Mary can put a check in any of the 6 boxes in the table, and that's her choice - the row shows which ribbon she picked, and the column shows which paper she picked. The number of boxes is 3 rows times 2 columns = 6 boxes. That's why you multiply. - Doctor Rick, The Math Forum http://mathforum.org/dr.math/
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