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SAT math

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Set M consists of the consecutive integers from -15 to y, inclusive. If the sum of all the integers in set M is 70, How many numbers are in the set?
SAT prep help - Anonymous, Saturday, September 28, 2013 at 3:16pm
a. 33
b. 34
c. 35
d. 36
e. 37

  • SAT math - ,

    There are y+16 integers. We just want to sum an arithmetic sequence where
    a = -15
    d = 1 and find how many terms there are:

    (y+16)/2 (-30+(y+15)*1) = 70
    y = 19

    So there are 19+16=35 terms

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