Question

Find the diameter of base of cylinder, if its height is 1.2 metre and its curved surface area is 31680 square centimetres.​

Answer 1

Height of cylinder = 1.2m = 120cm

Curved surface area of cylinder = 2πrh

31680 = 2πrh

31680 = $2 \times \frac{22}{7} \times r \times 120$

31680 = $\frac{44}{7} \times 120 \times r$

31680 = $\frac{5280}{7} \times r$

$31680\times {\frac{7}{5280}}$ = r

${}^{6} \cancel{{31680}} \times {\dfrac{7}{\cancel{5280}}}$ = r

r = $6\times7$

$\Large{r\:=\:42}$

‎

Diameter = 2r

d = $2\times42$

$\Large\boxed{d\:=\:84cm}$

Answer 2

Answer:

$\huge\colorbox{yellow}{Solution:-}$

Heighttt of cylinder = 1.2m = 120cm

Curved surface area of cylinder = 2πrh

31680 = 2πrh

31680 = 2 × 22/7 × r × 120

31680 = 44/7 × 120 × r

31680 = 5280/7 × r

31680 × 7/5280 = r

r = 6 × 7

r = 42

‎Diameter = 2r

d = 2 × 42

d = 84cm