#### • Class 11 Physics Demo

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# Free Answer to Math Riddles

Math Riddles:
Math riddles are basically based on the mathematical basic.Most of the Riddles questions are of logical thinking, tricky and reasoning type. Solving riddles helps in improving math skill level.

1. Find the value by making using mathematical code language.
21 ÷ 10*20 - 4 + 2

Solution: By making use of BODMAS operation we simplify the given sum.
= 21 ÷ 10 * 20 - 4 + 2
= 21 * 2 - 4 + 2
= 42 – 4 + 2
= 42 - 2
= 40

2. There are two numbers. Five times the first and four times the second are equal. Find the ratio of the sum of the squares of the         two numbers and their product.

Solution: Let the first number be a and the second number be b.
By making use of proportions.
5a = 4b

$\frac{a}{b}$ = $\frac{4}{5}$

= $\frac{a^{2}b^{2}}{ab}$ = $\frac{a}{b}$ + $\frac{b}{a}$

$\frac{4}{5}$ + $\frac{5}{4}$

= $\frac{41}{20}$

3. By what percent is 64 less than 80.

Solution: Required percentage = $\frac{80-64}{80}$*100

= $\frac{16}{80}$*100

= 20%

4. The average weight of 18 students in a class is 15 kg. If one student leaves the class, the average weight decreases by 0.8 kg. Find the weight of the student in kg.

Solution: Let the weight of the student who left the class be x kg.
Given total weight of 18 students = 270 kg
Total weight of 17 students = (17) (15-0.8)
= 241.4 kg
weight of student = (total weight of 18 students) - (Total weight of 17 students)
= 270 – 241.4
= 28.6 kg

5.  In a 100 m race. A beats B by 50 m or 10 seconds. Find the speed of A.

Solution: Given B travels 50 m in 10 seconds.

Speed = $\frac{distance\ traveled}{time\ taken}$

= $\frac{50}{10}$ = m/s

Time taken by B to complete the race = $\frac{1000}{5}$ = 200 s

Time taken for A = 200 - 10 = 190 s

Speed of A  = $\frac{1000}{190}$ = 5 $\frac{5}{19}$ m/s