for a given AP the 5th term is 20 and the 10th term is 35. find the sum of first 20 terms of this AP
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Answered by
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a5 = 20
a+4d=20. (1)
a10= 35
a+9d=35. (2)
ELIMINATION METHOD
a+4d=20
a+9d=35
-5d=-15
d=-15÷-5
d=3
putting value of d in equation 1.
a+4d=20
a+4×3=20
a=20-12
a=8
Sn = n/2 (2a+n-1×d)
S20=20/2 (2×8+20-1×3)
S20 = 10 (16+19×3)
S20 = 10 ( 16+57)
S20= 10×73=730 ans.
HOPE IT HELPS BUDDY
a+4d=20. (1)
a10= 35
a+9d=35. (2)
ELIMINATION METHOD
a+4d=20
a+9d=35
-5d=-15
d=-15÷-5
d=3
putting value of d in equation 1.
a+4d=20
a+4×3=20
a=20-12
a=8
Sn = n/2 (2a+n-1×d)
S20=20/2 (2×8+20-1×3)
S20 = 10 (16+19×3)
S20 = 10 ( 16+57)
S20= 10×73=730 ans.
HOPE IT HELPS BUDDY
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Answered by
1
Answer:
730
Step-by-step explanation:
- d=3
- a=8
- answer = 740
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