Four times the difference of a number and nine is -30

Answer 1

First write the difference of a number "n" and 9. Remember difference means subtract. So n -9.

Now note that problem states that 4 times this difference is -30. So multiply n-9 by 4. Remember to distribute the multiplication to both parts...so 4(n-9). This would be: 4n - 36.

Set this expression equal to -30

4n - 36 = -30. Adding 36 to each side gives:

4n = 6. Dividing each side by 4 gives:

n = 1.5

Think you are finished? Better check your answer!

Does 1.5 * 4 - 36 = -30? Yep!

Answer 2

Hi, Daniel,

Let the number be X. Write the sentence as it sounds:

"the difference of a number and 9" becomes (X - 9)

"Four times that number" means 4(X - 9)

"is 30" means = 30

Therefore, 4(X - 9) = 30

4X -36 = 30

4X = 66

X = 16.5

Try it: 4*(16.5-9)=30 ??

I hope this helps,

Bob