series - parallel (new)

[tdotboys]

Hi guys. please help me solving these 2 similar problems. i have the answere at the back of the book, but for some reason i am not able to figure this out.i will scan and post the answere aswell. looking for explanation. Thanks

[CraigFL]

First --

two 10 ohm in series = 20 ohm
one 10 ohm and one 20 ohm in series = 30 ohm
20 ohm and 30 ohm in parallel = 12 ohm
therefore, (c) , 10 ohm in series with 12 ohm = 22 ohm

Second--

two 10 ohm in series = 20 ohm
one 10 ohm and one 20 ohm and one 10 ohm in series = 40 ohm
20 ohm and 40 ohm in parallel = 13.33 ohm
therefore, (c) , 10 ohm in series with 13.33 ohm = 23.33 ohm

[tdotboys]

Thank you.