How does 9 and 10 = 21?
Number Theory
Level
2
The following expressions are possible ways of using 9 and 10 to get 21:
- 9 + 10 - 9 + 10 - 9 + 10
- ( 9 × 9 ) - 10 - 10 - 10 - 10 - 10
- 9 ( 9 + 10 ) - ( 10 × 9 ) - ( 10 × 9 ) + 10 + 10 + 10
- 9 + 10
- 9 × 10 - 9 + 10 - ( 9 × 10 ) + 10 + 10
- 9 + 10 + 10 + 10 - 9 - 9 ( -9 + 10 )
What is the sum of the #s of the 4 expressions that actually equal 21? (Assume the expressions were 1, 4, 5, and 6. Add them all up to get the answer you are looking for.)
16
13
12
7
15
18
9
10
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
1 solution
Only expressions 1 ,3,5,6 are giving 21 so adding the no 1+3+5+6=15 ,15 will be the answer.