Question

In an AP the first term is 1and common difference is 4 how many terms of AP shouldbe taken for their sum equal to be 120​

Answer 1

Answer:

a=1;

d=4;

Sum of terms =120;

•°• 120=n/2(2a+(n-1)d)

=> 120=n/2×2×1+4(n-1)

=> 120= n+4n-4;

=> 120+4=n+4n

=> 124=5n

=> n=124/5

=> n= 24.8

to prove that the sum of 24.8 terms is 120:-

sum= 24.8/2+(2×1+(24.8-1)4)

= 24.8/2×2+23.8×4

= 24.8+95.2

=120.0

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