ln(bcds): Math Challenge #1

ROB MACDONALD (fac.)

Editor’s note: we are proud to be the latest host to continue the math department challenge tradition, now in our new column, ln(bcds). Please email your responses to Rob MacDonald.

Middle School

Stacy is thinking of a three-digit prime number, and she says that if she multiplies all three of its digits together, she gets a prime number. She says that if she adds all three of its digits together, she also gets a prime number.

How many guesses would you need to figure out what Stacy's number is? Explain your answer.

Upper School

Fill in the blanks and explain your answer:
1, 10
0, 9
__, 60
11, __
15, 70
13, 66
17, 96

Hint: A little bit of searching on the web might make a big difference.

Again, please email your response to Mr. MacDonald. You may use the comments for discussion, but please don’t ruin the fun and give away the answers to everyone!