Question

the primary of a transformer connected to 170v has 10 turns. the secondary has 70 turns. find voltage. this is a step down transformer

Answer 1

No it isn't. (Unless you connect it backwards.)

If the primary has 10 turns and the secondary has 70 turns,
then the voltage that appears across the secondary is
7 times the voltage that you feed to the primary.

If you're 'exciting' the primary with 170 volts, then you need
to be cautious around the secondary terminals, because there's 
1,190 volts there !

If you want to use your transformer in a step-down configuration,
you can certainly connect it up the other way around.

Feed the 170 volts to the winding with 70 turns.  You've reversed
the labels 'primary' and 'secondary', and that's OK.  The voltage
at the terminals of the 10-turn winding will be (170/7) = 24.3 volts.