Play with Numbers

You have to make 100 by interspersing any number of pluses and minuses within the string of digits 9 8 7 6 5 4 3 2 1.
Note: You can’t change the order of the digits.


So what’s the least number of pluses and minuses needed to make 100?

Solution

To start, we can take the first two digits and make the number 98, which is quite close to 100. Thus, in this case, we add and subtract the remaining single digits to get 2, and we’ll have 100.

In fact, there are eight ways to do this:

98 + 7 + 6 – 5 – 4 – 3 + 2 – 1

98 + 7 – 6 + 5 – 4 + 3 – 2 – 1

98 + 7 – 6 + 5 – 4 – 3 + 2 + 1

98 + 7 – 6 – 5 + 4 + 3 – 2 + 1

98 – 7 + 6 + 5 + 4 – 3 – 2 – 1

98 – 7 + 6 + 5 – 4 + 3 – 2 + 1

98 – 7 + 6 – 5 + 4 + 3 + 2 – 1

98 – 7 – 6 + 5 + 4 + 3 + 2 + 1

This can also be done by using less than 7 ‘+’ and ‘-‘. 

That can be done by considering 1st six digits and make the numbers like 98, 76,54 and use the rest single digits. Like : 

98 – 76 + 54 + 3 + 21 = 100 

Here this can be obtained by using just four “+” and “-“.