191. What is the 5-digit number (including zero) in which the last digit is twice
the first, the second digit is the difference between the third and the first, and the fourth digit is the sum of the first and third added and then subtracted
from the fifth.

192. What is the largest number you can write using the digits 1, 2, and 3? Just the
digits, no other symbols.

3^{21} or 10,460,353,203.

193. Replace the @ symbols with standard mathematical symbols, like +, -, and x,
to make the following equation true:

9 @ 8 @ 7 @ 6 @ 5 @ 4 = 91

9 x 8 - 7 + 6 x 5 - 4 = 91.

194. There are 10 baskets. Each of
the 9 baskets have 10 balls weighing 10 kg each, except for one basket which has 10 balls weighing only 9 kg each. All the balls and baskets are identical in
appearance. You are asked to determine which basket contains the 9 kg balls. You can only take a single measurement using a weighing machine (the balls can be
taken out from the baskets but still you can only take one measurement). How would you do it?

Line up the baskets. Take 1 ball from the 1st basket, 2 balls from the 2nd, 3 balls from the 3rd and so on. Put them all on the weighing machine. If all the balls weigh 10 kg, their mass should add up to 550 kg. Thus, by subtracting the mass you get from 550 kg, you will know which basket they are in. For example, if the 9 kg balls are in basket 6, the scale will read 544 kg.

195. What rule am I using to determine the numbers in this series?

102 104
108 110
114 128

The series consists of prime numbers, starting at 101, plus one. Here are the original prime numbers: 101, 103, 107, 109, 113, 127.

196. What is the next number in this series;

18, 46, 94, 63, 52, ?

61. Each is a perfect square read from back to front.

197. What is the next number in the following series?

1, 2, 6, 30, 60, 180, 900, 1800,
5400 ?

27,000. The repeating pattern is, 2, 3, and 5 times the preceding number.

198. Somehow or other I got talked into buying something on the installment plan. I'm not sure I got a good deal. The payments to date, according to my checkbook, have reached $96. The second year cost $2.00 more than the first year; the third
year cost $3.00 more than the second; and the fourth year cost me $4.00 more than the third. What were my payments the first year?

199. Matt gave John as many dollars as John started out with. John then gave
Matt back as much as Matt had left. Matt then gave John back as many dollars as John had left, which left Matt broke and gave John a total of
$80.00. How much did Matt and John have at the beginning of their exchange?

Matt had $50.00 and John had $30.00.

200. There are several chickens and rabbits in a cage (with no other types of
animals). There are 72 heads and 200 feet inside the cage. How many chickens are there, and how many rabbits?

Let r = the number of rabbits and c = the number of chickens. Then, r + c = 72. 4r + 2c = 200. To solve, we multiply the first equation by 2, and then subtract it from the second equation. 4r + 2c = 200 (-) 2r + 2c = 144 thus 2r = 56 r = 28 c = 44; So, there are 28 rabbits and 44 chickens.