A dealer bought an item for $7, sold it for $8, bought it back for $9, and sold it again for $10. How much profit did she make?
Fifty-six biscuits are to be fed to 10 pets: each pet is either a cat or a dog. Each dog is to get six biscuits, and each cat is to get five. How many dogs are there?
You inherit a large crate of mangos. The top layer has 18 mangos. Peering through the cracks in the side of the crate, you estimate there are five layers of mangos inside. About how many mangos did you inherit?
One hundred people in your neighborhood always drive to work between 7:30 and 8:00 am and arrive 30 minutes later. Why must two people always arrive at work at the same time, within a minute?
If a is the smallest prime number greater than 21 and b is the largest prime number less than 16, then ab =
Fill in the blanks in the following congruences with any correct answers other than the number itself:
____ ≡ 6 (mod 7); ____ ≡ 5 (mod 12); _____ ≡ 3 (mod 5).
Find the first 15 pairs of twin primes.
Consider the list of numbers: 2n – 1, where n first equals 2, then 3, 4, 5, 6….
What is the smallest value of n for which 2n – 1 is not a prime?
Suppose today is Tuesday, October 12. Which day of the week will it be 147 days from now?
Express each of the following natural numbers as a sum of distinct, nonconsecutive Fibonacci numbers: 43, 90, 2000, 609.