1.

The first term of an A.P. is 5, the last term is 45 and sum is 400. Find the number of terms and the common difference.

Answer» `" "a = 5`
`" "a_n = 45`
`" "S_n = 400`
`rArr (n)/(2) (5+ 45) = 400`
`50 n = 800`
`n = 16`
also `a_n = 45`
`5 + 15 d = 45`
` 15 d = 40`
`d= 8//3`


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