rearranging Formula: Make b the subject of this formula 7a=b/5-3(bc+2)

[Rachellowes]

question: Make b the subject of this formula 7a=b/5-3(bc+2)

This is my attempt so far...

Multiply by 5: 35a=b-15(bc+10)

multiply out the brackets: 35a=b-15bc-30

Take out b as a common factor: 35a = b-15c-30

plus 30: 35a+30=b-15c

plus 15c: 35a +30+15c=b

Switch the sides: b = 35a + 30 +15c

Is this correct? unsure of the bottom half of my working.

Thanks

 

[Deleted member 4993]

question: Make b the subject of this formula 7a=b/5-3(bc+2)

This is my attempt so far...

Multiply by 5: 35a=b-15(bc+2)

multiply out the brackets: 35a=b-15bc-30

Take out b as a common factor: 35a = b-15c-30........ ?

Collect terms with 'b' on one side of the equation:

35a + 30 = b - 15bc

Take out b as a common factor (on the right hand side ) and Take out 5 as a common factor (on the left hand side )

5 * (7a + 6) = b * (1 - 15c)

b = 5 * (7a + 6)/(1 - 15c)


plus 30: 35a+30=b-15c

plus 15c: 35a +30+15c=b

Switch the sides: b = 35a + 30 +15c

Is this correct? No .... see above

unsure of the bottom half of my working.

Thanks

.

 

[SallyAnne]

So what happens next??

******** you were ok up to here

Next step makes no sense; should be:
35a = b(1 - 15c) - 30

Make sure you understand why...

this is very helpful, but what happens after this stage?

thank you

 

[stapel]

Next step...should be:
35a = b(1 - 15c) - 30

Make sure you understand why...

this is very helpful, but what happens after this stage?

You need to get "b" by itself. If they'd given you "35a = 2b - 30", what would you do next? Do the same thing here.