Can you please explain to me what I did wrong in this?

Question

This is the equation:

-2.5(a+2a)=22.5

Ok so first I did this

-2.5(3a)=22.5 (combined 2a and a)

Then I did

22.5+-2.5 and I got 20 (added -2.5 to both sides)

3a= 20

Then I divided

and got 6.66666666... I rounded it to 7.

What's wrong with this?

Answer 1

well tried ....
you started ....very well ..
-2.5 (3a ) =22.5
but in the next step you done one silly mistake ..
on right side -2.5 is multiplied with 3a ..so we divide both side by
-2.5 not add -2.5 both side ...

so divide -2.5 both side
we get 3a = - 9

again divide both side by 3

we get a =- 3 ...as final answer ..
hope this will help you ..

Answer 2

Your problem was with order of operation.

I think someone else already did this but I will try to explain more.

First you do what is in side of the parens.

a+2a = 3a

Gives you
-2.5(3a)=22.5

You still have to get rid of the Parens:

-2.5(3a) is the same as -2.5 * 3 * a

Then next is the multiplication:

Gives you
-7.5 * a = 22.5 which is the same as -7.5a = 22.5

Now you have to do the division:

a = 22.5 / -7.5

a = -3

Answer 3

Well..let's walk through this

-2.5(a+2a)=22.5

First get rid of the parenthises

-2.5(3a)=22.5 (i combined like terms to get 3a, 2a+a equals 3a)

-7.5a=22.5 (i used the distributive property to get rid of
parenthises)
Now to get a alone, undo this operation, so divide both sides by 7.5

-7.5a=22.5
____ ____
7.5 7.5

a= 3

here's what you did wrong-
when you said you added -2.5 to 22.5-you should not have done that. it should have been 22.5 DIVIDED by -2.5. why? because if you are multiply -2.f by what is inside the parenthisis, you do the OPPOSITE operation to get rid of it, so you divide. if you were adding -2.5 then only would add it to -22.5,

Hope i helped!

Answer 4

Where you had
-2.5(3a) = 22.5 you should have multiplied
-7.5a = 22.5 then divide
a = 22.5/-7.5 = -3
(for future reference, don't round to the nearest whole number if you get fractions or decimals - a fraction or decimal is a perfectly acceptable answer)

Answer 5

-2.5(a+2a)=22.5
-2.5(3a)=22.5
-7.5a = 22.5 (multiplied -2.5 and 3a)
a= -3 (divided both sides by -7.5)

Answer 6

-2.5 ( a + 2a ) = 22.5
-2.5 ( 3a ) = 22.5
-7.5 ( a ) = 22.5
-7.5 / -7.5 ( a ) = 22.5 / -7.5
a = -3