Here’s this week’s practice question– good luck, we’ll be posting the answer tomorrow!

How many integers between and are such that the sum of their digits is ?

- 190
- 210
- 211
- 230
- 231

Update: Answer/explanation post!

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By Margarette Jung on February 20, 2012 in Challenge Questions, Combinations and Permutations, Math Concepts, Math Multiple Choice, Math Question Types, Practice Question of the Week, Probability

Here’s this week’s practice question– good luck, we’ll be posting the answer tomorrow!

How many integers between and are such that the sum of their digits is ?

- 190
- 210
- 211
- 230
- 231

Update: Answer/explanation post!

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231

one digit nos adding to 2 (only 2) => 1

2 digit nos(11,20) => 2

3digit nos(101,110,200) => 3

4 digit nos(1001,1010,1100,2000) => 4

similarly

————————————–

20 digit nos will be =>20

21 digit nos will be =>21

Answer is 1+2+3+…….+20+21 = 231

231 only if you consider two 1’s and 251 if you include two 1’s and one 2

1+2+3+….+21 = 231

231