Question

18. The first term of an A.P is 5 and the last term is 145. Find the number of terms it
their sum is 600​

Answer 1

a=5

an=145

n=?an=?sn=600

✓a+4d=5 first equation

✓a+144d=145 second equation

solve this equation by elimination method we get:

a gets cancelled left with

d=1

similarly if you solve a you will get equal to 1

an=(a+n-1)d

145=(5+n-1)1