If the cost of making a leather ball is Rs.431.20 at the rate of Rs.17.50 per square cm. Calculate the length of diameter of the ball.

Explanation

Let the radius of the ball =r cm.
`therefore` the whole surface area of the ball `=4pir^(2)` sq-cm.
Rs. 17.50 is required to make a ball of leather of 1 sq. cm .
`therefore ` Rs. 431.20 is requied to make a ball of leather of `(431.20)/(17.50) sq. cm.`
`therefore 4 pir^(2) =(431.20)/(17.50)` or ` 4 xx(22)/(7)xxr^(2) =(4312)/(175)`
or, `r^(2)=(4312)/(175xx4xx22) =(49)/(25)` or , `r=sqrt((49)/(25))=7/5=1.4`
`therefore ` the diameter of the ball `=2xx 1.4 cm =2.8 cm`