is this equation correct?

Question

240=2(9L/10+6B/5)
120=9L+6B/10
1200=9L+6B

plzz just tell me whethere it is correct upto here or not..
if it is yes then where did the 10 below 9L go
i.e 9L/10

Answer 1

No, you made a few mistakes:

1) In the first equation you divided both sides by 2 AND distributed the 2 through the parentheses. You only have one "2" here, so you can't do both. Either divide both sides by 2, and get 120 = (9L/10 + 6B/5), or distribute the 2 and get 240 = (9L/5 + 12B/5).

2) Remember the distributive rule: a(b+c) = (ab+ac). In the second equation it looks like you tried to distribute the "2" to the first term (9L/10) but not the second term (6B/10).

3) Even if we assumed the second equation was right, the third still shows a wrong calculation. When you multiplied both sides by 10, the left would become 1200 and the "10" under 6B/10 would go away, but you'd still have to multiply the 9L by 10. Again, you have to follow the distributive rule.

So if you start again:

240=2(9L/10+6B/5)

Divide both sides by 2:

120 = (9L/10+6B/5)

Now multiply both sides by 10:

120*10 = (9L/10 + 6B/5)*10
1200 = (10*9L/10 + 10*6B/5)
1200 = (9L + 12B)

Answer 2

The reasoning is not correct. When you divide both sides of the first equation by 2, you get 120=(9L/10)+(6B/5). Multiplying both sides by 10, you get 1200=9L+12B. Simplifying, you get
400=3L+4B.

Answer 3

240 =2(9L/10+6B/5)
240 = 2 [10(9L/10)+(6B/5)10]
[cancel 10 then cancel 5, replace 10 with 2]
240 = 2 (9L + 12B)
240 = 18L + 24B
.....................

Answer 4

240=2(9L/10+6B/5)
240/2=9L/10+6B/5
120=9L/10+6B/5
120=9L/10+12B/10
10(120)=9L+12B
1200=9L+12B
400=3L+4B