Find the real solution(s) by solving for x (round any decimals to the nearest 100th); 5x = 320
2 answers:
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You can treat it as an arithmetic sequence, so multiply the average integer value by the number of integers:
(40+12)/2 × (40 -12 +1) = 26×29 = 754
You can subtract the sum of integers 1–11 (66) from the sum of integers 1–40 (820) to get the sum of integers from 12–40: 820 - 66 = 754.
You can let a graphing calculator do it. (See attached.) This method takes perhaps the least amount of thought. It, too, gets a sum of 754.
(40+12)/2 × (40 -12 +1) = 26×29 = 754
You can subtract the sum of integers 1–11 (66) from the sum of integers 1–40 (820) to get the sum of integers from 12–40: 820 - 66 = 754.
You can let a graphing calculator do it. (See attached.) This method takes perhaps the least amount of thought. It, too, gets a sum of 754.