গাণিতিক যুক্তি · ২১টি প্রশ্ন · পৃষ্ঠা ১/২
১. Two pipes fill a tank in 20 and 30 minutes; a drain empties it in 15 minutes. If the tank is half full, and the pipes and the drain are opened together, how long will it take to fill the tank?
২. A viral post's share-count starts at 3. Each next value equals twice the previous minus 1. Find the 5th term.
৩. What is the minimum number of plants one should have so that they can be arranged in 12, 15 or 18 rows and also be arranged in equal number of rows and columns?
৪. A litt serves floors 1 through 16, moving one floor every 12 seconds. It walts 48 seconds at both endpoints. It can complete how many round trips from 9.00 AM to 3 : 20 AM?
৫. What should be the ratio of sugar in a mixture costing BDT 50 per kg and BDT 55 per kg, such that there will be 10% profit if the mixture is sold for BDT 60 per kg?
উত্তর যাচাই করো — গণনায়: ৬০ টাকায় ১০% লাভে ক্রয়মূল্য = $60/1.1 = 54.545$; alligation-এ ৫০-চিনি ও ৫৫-চিনির অনুপাত = $1:10$ (যাচাই: $(1\times50+10\times55)/11 = 600/11 = 54.545$)। সঠিক উত্তর B (1:10), কিন্তু keyed answer C (10:1) উল্টানো — keyed answer সন্দেহজনক।
৬. In triangle ABC, the external bisectors of the angles B and C intersect at point O. If angle A is 90 degrees, then the measure of the angle BOC is
৮. A circle is inscribed in a right triangle whose legs measure 9 and 12. Find the radius of the circle.
৯. In a geometric progression, the 3rd term is 12 and the 6th term is 96. Find the sum of the first 8 terms.
১০. The present age of a father and his son are in ratio 7 : 2. Five years ago the ratio was 6 : 1. Find the sum of their present ages.
১২. For x > 0, what is the minimum value of x+ 16 x ?
উত্তর যাচাই করো — গাণিতিকভাবে x>0 এর জন্য x+16/x এর ন্যূনতম মান AM-GM অনুসারে 2√16 = 8, যা কোনো অপশনেই নেই। এছাড়া A ও B উভয় অপশনই '4' (একটি ইংরেজি, একটি বাংলা অঙ্কে)। keyed answer B (৪) ভুল/সন্দেহজনক।
১৩. A cistern is normally filled in 6 hours, but a leak makes it take 8 hours. How long would the leak alone take to empty a ful cistern?
১৪. Nasif's watch gains 4 minutes per hour. It was correct at 2:00 pm yesterday. When it displays 6:00 am today. What is the accurate time?
১৫. ab is negative and a2+b2 is greater than o, but less than 114. What is the minimum value of ab?