Question

Help me solve this equation

Answer 1

So basically since it already has a common denominator all you have to do is subtract 9 from 4 and get 5

Answer 2

A/15 + 4/15 = 9/15

First, basically we need to know what adds into 4 to equal 15 since the denominators are the same. This is a quite easy question and can be answered in your head. I suppose I'll show you the way that most schools want their students to learn how to do this. To get started, we need to simplify 9/15. To do so, we need to find the GCF. 

Factors of 9: 1, 3, 9
Factors of 15: 1, 3, 5, 15

Out of both lists of factors, we can tell that 1 and 3 are the common numbers between them. Since we are looking for the GCF, the greatest number would be 3. The GCF is 3. 

Second, we can divide the numerator (9) and denominator (15) by the GCF we recently found which was 2.
$9 \div 3 = 3 \\ 15 \div 3 = 5$

Third, we can now put our two quotients we just solved into fraction form. The simplified fraction should be: $\frac{3}{5}$ . Now that we are done with simplifying fractions, we can move back to the problem. Our next step would be to join the denominators between the two fractions we are adding.
$\frac{a + 4}{15} = \frac{3}{5}$

Fourth, since we need to get 'a' by itself, we need to move everything to one side of the problem. Our first step to doing this is to multiply each side by 15.
$a + 4 = \frac{3}{5} \times 15$

Fifth, we need to focus on multiplying 3/5 times 15. To do this, take the numerator of the fraction (3) and times it by 15 to give you 45. We do not do this to the denominator (5). Your new fraction should look like: $\frac{45}{5}$ . This can be simplified down to get a whole number. To solve that, you can set up long division or ask yourself, what times 5 equals 45? The answer is 9.
$a + 4 = 9$

Sixth, once again, we need to move everything away from the 'a' so it can be by itself. Subtract 4 from both sides and solve 9 - 4. You should have gotten 5, which is the answer. 
$a = 5$

Answer: $\fbox {a = 5}$