New Problems: Math Stinger #156

Your calculator is not working properly - it cannot perform multiplication. But it can add and subtract any two numbers. It can also compute x-1 and x2 of any number x. Can you nevertheless use this defective calculator to multiply two numbers?


Math Stinger #155

In a math class, 21% of the students get an A and 81% of those A students are part-time students. Among part-time students, 31% of them do not get an A. What percentage of the whole class are part-time students?

Please send solutions to tchan4 at kennesaw dot edu.


Math Stinger #154

A piece of paper is divided into four rectangles as shown below. It is clear that the one at the bottom-left corner has the largest area and the one at the top-right corner has the smallest area. Without making measurements, how can we decide which of the other two rectangles has the larger area?

partitioned rectangle

Please send solutions to tchan4 at kennesaw dot edu.

Math Stinger #153

There are 6 students, each has an item of gossip known only to himself/herself. Whenever a student calls another, they exchange all items of gossip they know. What is the minimal number of calls they have to make in order to ensure that very one of them knows all the gossip there is to know? Justify your answer.

Please send solutions to tchan4 at kennesaw dot edu.


Older Stinger Problems

Math Stinger #152

Without using any calculator or computer, determine (with justification) which of the following two quantities

1.0000000001 + 1 / 1.0000000001


0.9999999999 + 1 / 0.9999999999

is bigger?

Math Stinger #151 
Going at top speed, Grand Prix driver x leads his rival y by a steady three miles.  Only two miles from the finish, x runs out of fuel.  Thereafter x's deceleration is proportional to the square of his remaining velocity, and, in the next mile, his speed exactly halves.  Who wins, and why?

Math Stinger #150
Let us assume that a given pair of people either know each other or are strangers.  If six people enter a room, show that there must be either three people who know each other pairwise or three people who are pairwise strangers. 

Math Stinger #148
For two given positive integers n and k, how many different sequences of positive integers a1 ≤ a2 ≤ a3 ≤ ... ≤ ak are there in which ak ≤ n?

Older solutions published to: Solved Stingers