Given :6 years later Ravi's age is 25 years.To do :We have to find the present age of Ravi.Solution :Let the present age of Ravi be x years.This implies,Age of Ravi after 6 years $= x+6$$x+6 = 25$$x=25-6$$x=19$The present age of Ravi is 19 years.

Hydrogen is mostly classified as a nonmetal because it has many of the properties of nonmetals. For example, it is gas at room temperature. Hydrogen shares properties with the alkali metals in group 1. In liquid form, hydrogen conducts electricity just like metal does.therefore it is difficult to assign hydrogen as ... Read More

Material is any substance or mixture of substances that occupy space, has a volume and has a mass. We need to group materials for our convenience and to study their properties. These properties are• Appearance.• Solubility.• Hardness.• Float/sink.• Transparent/opaque.

Given :15 years later Mohan's age is four times the present age.To do :We have to find the present age of Mohan.Solution :Let the present age of Mohan be x years.This implies, Age of Mohan after 15 years $=$ 4x$x+15 = 4x$$4x-x=15$$3x=15$$x=\frac{15}{3}$$x=5$The present age of Mohan is 5 years.Read More

Given :When a number is tripled and 2 is added to it the result is 14.To do :We have to find the number.Solution :Let the number be x.This implies,$3x+2 = 14$$3x=14-2$$3x=12$$x=\frac{12}{3}$$x=4$ Therefore, the number is 4.

Given :The present age of the person $=$ 15 years.To find :We have to find his age 4 years ago.Solution :The age of the person 4 years ago $= 15 - 4$ years $= 11$ years. Therefore, the age of the person 4 years ago was 11 years.

Tearing of paper is a physical change because on sticking back the paper together we get the original material back i.e the whole paper.

Given :The given statement is 'The sum of a two-digit number and the number obtained by reversing the digits'.To do :We have to find the sum is always divisible by which number.Solution :Let the two digit number be $10x+y$.The number obtained by reversing the digits is $10y+x$.The sum of the ... Read More

Given :The ratio of ages of son and father $= 1:3$.The age of the son $= 10$ years.To do :We have to find the age of the father.Solution :Let the age of the father be x years.Therefore, $1:3=10:x$$\frac{1}{3}=\frac{10}{x}$$x(1) = 10 (3)$$x = 30$Therefore, the age of the father is 30 ... Read More

Sum of two prime numbers: All the prime numbers except 2 are odd numbers.The sum of two odd numbers is an even number.Therefore, the sum of two prime numbers $(>2)$ is an even number.So, option (B) is correct.