The slant height of a cone is increased by 10%. If the radius remains the same, the curved surface area is increased by (a)   10%      (b)  12.1%             (c)  20%         (d)  21%

Explanation

Let the slant height of the cone be `l`

C.S.A of cone=`(pi)rl`

So, new slant height = `l+10/100xxl`=`1.1l`

`therefore` New C.S.A of cone=`pixxrxx1.1l`

Percentage increase in curved surface area = (New C.S.A - initial C.S.A / Initial surface area)`xx100`

`(1.1pirl-pirl)/(pirl)xx100`=`10%`

Hence, option(a) is correct.