Practice Quiz

SAT Math

Category - Number and Operations

Start a Study Session Sign up for Question of the Day
What is the sum of all 2-digit odd numbers?
  1. 755
  2. 1,255
  3. 2,475
  4. 2,955
  5. 3,075
Explanation
Answer: C - The sum of all 2-digit numbers is 2,475. Two-digit odd numbers form an arithmetic sequence.
a_1 = 11,d = 2,a_n = 99,n = (99-9)/2 = 90/2 = 45
S_n = n/2 (a_1 + a_n ) = 45/2 (11 + 99) = 45/2×110 = 45×55 = 2,475
Previous Next
Was this helpful? Upvote!
Login to contribute your own answer or details
Start a Study Session Sign up for Question of the Day

Top questions

Related questions

Most popular on PracticeQuiz