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(#M40020296) BOOK question Progression sum Keep an EYE

find the value of the expression : 1 - 4 + 5 - 8 ... to 50 terms....

Asked In Book (11 years ago)

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ABDUL ODUD  (11 years ago)

1-4+5-8.....to 50 terms
as common diff between 1 and -4 is -3 and +5 and -8 is -3 ,so total 25 terms ...and 25*-3=-75
or
1 - 4 + 5 - 8 ... to 50 terms....
= (1 + 5 + 9 + ... 25 terms) - (4 + 8 + 12 + ... 25 terms)
= ( 1 + 5 + 9 + ... + 97) - ( 4 + 8 + 12 + ... + 100)
= [(25/2)(1+97)] -[(25/2)(4+100)]
= 25(49 - 52)
= -3*25
= -75

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Vinay Sipani   (11 years ago)

1 - 4 + 5 - 8 ... to 50 terms....
= (1 + 5 + 9 + ... 25 terms) - (4 + 8 + 12 + ... 25 terms)
= ( 1 + 5 + 9 + ... + 97) - ( 4 + 8 + 12 + ... + 100)
= [(25/2)(1+97)] + [(25/2)(4+100)]
= 25(49 + 52)
= 101 * 25
= 2525

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