Problem: During the next Tree Plantation Week, Mutual Trust Bank is considering planting trees in one of its own rectangular piece of land which is 90 feet long and 66 feet wide. This surrounded by boundary wall of 5 feet height. It has been decided that trees will be planted leaving 5 feet laud free from the wall in all four sides. It was also decided that the distance from one tree to another in both row and column will be 4 feet. What is the maximum number of trees that can be planted in the land?

Correct Answer:  315

Explanation:

মনে রাখবেন দেয়ালের দূরত্ব দৈর্ঘ্য এর দুই পাশ এবং প্রস্থ এর দুই পাশ থেকে বিয়োগ করতে হবে । সম্ভাব্য সারি এবং কমানোর জন্য 1 করে যোগ হবে কারণ শুরুতে একটি করে গাছ আছে । Maximum গাছ লাগানোর সংখ্যা –সম্ভাব্য সারি x কলাম ।

Given that, the length of the land = 90 feet.

According to the question, possible length of the rectangle for plantation = 90 – 5 x 2 = 80 feet.

And, width of the rectangle for plantation = 66 – 5 x 2 = 56 feet.

Possible row = $\frac{56}{4}$ + 1= 15 and possible column = $\frac{80}{4}$ + 1 = 21.

Maximum tress = 21×15 = 315.