1.

The value of `sum_(i=1)^(n)sum_(j=1)^(i)sum_(k=1)^(j)=220` , then the value of `n` equalsA. `11`B. `12`C. `10`D. `9`

Answer» Correct Answer - C
`(c )` `sum_(i=1)^(n)sum_(j=1)^(i)sum_(k=1)^(j)1`
`=sum_(i=1)^(n)sum_(j=1)^(i)j`
`=sum_(i=1)^(n)(i(i+1))/(2)`
`=(1)/(2)sum_(i=1)^(n)(i^(2)+i)`
`=(n(n+1)(n+2))/(6)=220`
`:.n=10`


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