Do you understand that a+a+a means one a plus another a plus yet another a? That gives you three a's. You can deduce that 3 a's + 5 = 20. So what is the value of "3 a's"? From that conclusion can you decide what the value of one a is? Once you find what the value of one a is, put that value back into the original equation in place of each "a" and see if the equation is true. If it is, you have the correct value of "a". If not, show us your work and we will try to help.
Here's what you need to realize:
a + a + a is equal to 3 * a.
Now, if we look back at the equation:
3*a + 5 = 20
Both sides of the equation are equal, so if we subtract 5 from both sides, they will still be equal.
3*a + 5 -5 = 20 -5
The +5 on the left side of the equation is gone, and the right side of the equation is now 15.
3*a = 15
Divide both sides by 3 to find the value of a.
3*a / 3 = 15 / 3
a = 5
Since you're dealing with a second-grader who almost certainly hasn't taken algebra, simplify: instead of letters, use shapes; say, boxes. :idea:
If three boxes, plus five things (beans, pennies, whatever) loose on the table, give you a total of fifteen things, then how many things would you have left if someone takes away the five loose things?
If this smaller amount left is split "fairly" between the three boxes, then how many things are in each box?
The number inside each box is the value they're looking for. :wink: