Question

an iron pipe 20 cm long has exterior be equal to 25 CM if the thickness of the pipe is 1 cm find the whole surface of the pipe

Answer 1

$\huge{Hey \:mate}$
Height of pipe = 20 cm
External diameter = 25 cm 
External radius = 25/2 = 12.5 cm
Internal diameter = 25 - (1 + 1)
= 23 cm
Internal radius = 23/2 = 11.5 cm

Let the external radius be R and the internal radius be r.
Total surface area of the pipe = 2πh(R + r) + 2π(R² - r²)
⇒ 2*22/7*20(12.5 + 11.5) + 2*22/7*{(12.5)² - (11.5²)
⇒ (44*480)/7 + (44*24)/7
⇒ 21120/7 + 1056/7
⇒ 22176/7
= 3168 cm²
The TSA of the pipe is 3168 cm²