All ACT Math Resources
Example Question #1 : How To Add Odd Numbers
Add the ones digits:
Since there is no tens digit to carry over, proceed to add the tens digits:
The answer is .
Example Question #2 : How To Add Odd Numbers
At a certain high school, everyone must take either Latin or Greek. There are more students taking Latin than there are students taking Greek. If there are students taking Greek, how many total students are there?
If there are students taking Greek, then there are or students taking Latin. However, the question asks how many total students there are in the school, so you must add these two values together to get:
or total students.
Example Question #2 : Even / Odd Numbers
Find the sum of 13 and 19.
Rewrite the question in a mathematical expression.
Add the ones digit.
Since this number is larger than , carry over the in tens digit when adding the next term.
Add the tens digit with the carry over.
Combine the tens digit and the ones digit. The answer is .
Example Question #3 : Even / Odd Numbers
In order to get an odd result from an addition, we must have one odd and one even number, thus you know from the first point about that only one of the two values is odd. Now, to get an even result, you can have two evens or two odds. So, let's presume that has two odd values, this means that must be even. Thus, you have:
Now, if we presume that has two even values, we must then know that is odd. Thus, we have:
First of all, you can eliminate the two answers that say that a given value is positive or negative. This cannot be told from our data. Next, it cannot be the case that is even. It will always be odd (hence, the correct answer is this). Finally, it cannot be that is even always. In the second case above, you will have two even numbers added together, given you an even. Then, you will add in an odd, giving you an odd.