Progressive Countdown

If you’re given a number, subtract 1, then 2 from the result, then 3 from that result and so on until you reach 0 or a negative number.

For example, if you’re given 15:

15 – 1 = 14
14 – 2 = 12
12 – 3 = 9
9 – 4 = 5
5 – 5 = 0

Which of these numbers will finish exactly at zero?

102 103 104 105 106

Show the answer »

105105 – 1 = 104
104 – 2 = 102
102 – 3 = 99
99 – 4 = 95
95 – 5 = 90
90 – 6 = 84
84 – 7 = 77
77 – 8 = 69
69 – 9 = 60
60 – 10 = 50
50 – 11 = 39
39 – 12 = 27
27 – 13 = 14
14 – 14 = 0

105

105 – 1 = 104
104 – 2 = 102
102 – 3 = 99
99 – 4 = 95
95 – 5 = 90
90 – 6 = 84
84 – 7 = 77
77 – 8 = 69
69 – 9 = 60
60 – 10 = 50
50 – 11 = 39
39 – 12 = 27
27 – 13 = 14
14 – 14 = 0

Posted in Brain Teasers

2 Comments on "Progressive Countdown"

? says
April 29, 2017 @ 03:41

I got this one right- who else????

Vishal Garg says
May 1, 2017 @ 01:49

There is a logic behind solving this problem.
You have to check the sum of 1 to n numbers by formulla,
sum = n*(n+1)/2
Now start putting n from 1 and you will get your answer.