a ring shape metal plate has an internal radius of 7cm and an external radius of 10.5.if the cost of material is rupee 5 per sq.cm,find the cost of 25 rings?
Find the external circumference first. Then find the internal circumference. Subtract the enternal from the the external and multiply the result by 5 rupees. Finally, multiply that result by 25 rings to give you the final cost.
I noticed that the cost is per sq. cm., which means you have to find the external and enternal AREAS and subtract one from the other. A=2Pi r^2. The rest would be the same.
