Given A.P = 3,8,13,...,253
Common difference = 8-3 = 5
The AP from the end = 253, 248,245,...,13,8,3
First term from the end = 253
Common difference = 248-253 = -5
We know that
an = a+(n-1)d
t20 = 253+(20-1)(-5)
→ t 20 = 253 +(19)(-5)
→ t 20 = 253-95
→ t 20 = 158
20th term from the end of the AP = 158