The next number should be 13112221. Why?
Because each of these numbers describes the previous number. Starting with 1, the 2nd line is 11 (one one), then the 3rd line describes 11 as 21(two ones). Then the 4th line is 1211 which describes (one 2, one 1). And so forth...
A hundred stones are placed, in a straight line, a yard distant from each other. How many yards must a person walk, who undertakes to pick them up, and place them in a basket stationed one yard from the first stone?
To collect the stones, the person must walk 1 yard to pick up the first stone, and then they had to double the distance each time - 2 yards, 4 yards, 8 yards etc.
To find the answer we multiply 202 by 50 = 10,100 yards.