Answer: 1) Third Option is correct.
2) Second Option is correct.
Step-by-step explanation:
Since we have given that
odd numbers are as follows:
1, 3, 5, .........................
so, first term = a = 1
d = common difference = 3-1=2
n = number of terms = 40
As we know that it forms an "Arithmetic Progression ":
[tex]a_n=a+(n-1)d\\\\a_n=1+(40-1)2\\\\a_n=1+39\times 2\\\\a-n=1+78\\\\a_n=79[/tex]
so, the fortieth odd number is 79.
Hence, Third Option is correct.
Now, we need to find the first forty odd numbers :
As we know the formula :
[tex]S_n=\frac{n}{2}(2x+(n-1)d)\\\\S_{40}=\frac{40}{2}(2\times 1+(40-1)2)\\\\S_{40}=20(2+39\times 2)\\\\S_{40}=20(2+78)\\\\S_{40}=20\times 80\\\\S_{40}=1600[/tex]
Hence, Second Option is correct.
