My brain is fried & im stuck

[JAWS]

Been studying hard but not hard enough it seems, last week I was finding these ok to do but I’m completely lost, it’s as if I’ve had brain freeze.

I divided 1 over 9 and 1 over 8 got to the o.236 but how do I get to 11.24 ohms by adding 7.

Thank you

 

[Gaz92552]

1 divided by 0.2361 gives you 4.24 add the 7

 

[JAWS]

Thank you Gaz appreciate it.

 

[kris jones]

personally i use the product over sum method here. r1 = 9 ohms and r2=8 so do r1xr2 = 72 then divide that by r1+r2 = 17 which = 4.23 now you done that they are in series together so you only have to add r3 to = 11.23 (series resistances are just added). now its ohms law. I=v/r which is 30v divided by 11.23 which is 2.67

note product over sum method only works with 2 parallel resistors. if you have say 4 in parallel you would work out the first 2 and then the second 2 and do the same when you have those down to just 2 in parallel to get one resistance

make sense?