The first option is your answer.
Sigma notation is just a fancy way to shorten a sum of a series of numbers using a set equation. The "n =" tells you where to start in the sequence and the top number tells you where to stop.
To find a number in between you could multiply 39/130 by 2/2
and 40/130 by 2/2 to get
78/260 and 80/260
Answer:
The first digit of a two digit number can be any of digits 1 - 9. It cannot be 0 though. Therefore there are 9 possible digits for the first place.
There are 5 possible digits for the second position. The two digit number has to be odd and therefore the final digit must be 1,3,5,7 or 9
Therefore for each and every one of the nine first digits there are 5 digits that the second can be.
Therefore ANSWER = 9 * 5 = 45 possible permutations.
2. The largest two digit number = 99
Subtract 57 and you get 42
ANSWER = 42
The forty two numbers are 58 ,59, 60, 61......98, 99
