Answer: The clock skip 0.25 seconds every 30 minutes.
Explanation:
Since we have given that
Clock was correct on Wednesday at 4 pm.
At 2 pm , on saturday, the clock was running late by 35 seconds.
From 4 pm wednesday to 4 pm thursday = 24 hours
From 4 pm thursday to 4 pm friday = 24 hours
From 4 pm friday to 2 pm saturday = 22 hours
So, total hours = 24+24+22 = 70 hours
We need to find the number of seconds that the clock skip every 30 minutes.
So, it becomes

Hence, the clock skip 0.25 seconds every 30 minutes.