221. Arrange the ten digits 0 to 9 in three arithmetical sums, using three of the four operations of addition, subtraction, multiplication, and division, and
using no signs except the ordinary ones implying those operations. Here is an example to make it quite clear (note that the example is not correct):
3 + 4 = 7 9 - 8 = 1 5 X 6 = 30
222. Several cartons of candy are being shipped from a manufacturer to warehouses where they will be prepackaged to sell to stores. The candy in each carton needs to be divided equally among 3, 4, 5, or 7 stores. What is the least number of pieces of candy that each carton can have?
223. Kevin flew to Puzzleland at the fantastic speed of 1000 miles per hour. There he picked up his friend and flew back, burdened by the extra weight, at only 500 miles per hour. What was his average speed?
226. There are 7 tennis balls which are identical in all aspects except that one of them weighs slightly less than the other 6. How can you identify the one that weighs less on a balance scale with no more than 2 separate weighings?
228. Can you arrange the odd digits 1, 3, 5, 7, and 9, and the even digits, 2, 4, 6, and 8, in such a way that the odd ones add up to the same as the even ones? You can use arithmetical signs and decimals, but the idea is to try and arrive at the simplest possible solution. There are, of course, many possible answers.
229. Many years ago when gasoline was only 46 cents a gallon, I stopped to fill up my car. I gave the attendant a $20.00 bill and waited for my change. Unexpectedly, he charged me for the number of gallons that the car needed instead of the dollar amount. (for example if the car took 8.4 gallons he would have charged me $8.40. Because he did this, I received less in change than I should have. The funny thing is that I had received in change exactly the amount that I should have been charged for the gas in the first place. Remembering that the cash indicator on a gas pump will only charge to the nearest half-cent, how many gallons of gas did I buy that day?
230. What is the four-digit number (no zeros) in which the third digit is the number of "winds," the first digit is one-half of the third, the second digit is double the third and the last digit is one-half the sum of the first three?