Solve Quantitative Aptitude question using substitution method

            Question : Ages of A and B are in the ratio of 7:4 after five years the ratio of the age is becomes 11:7.                  Find the age of A?

                 a) 12      b) 14     c) 15     d) 28

if you are following the traditional method to find the age of A will take around 60 seconds ,but if you are using the smart substitution method it will be solved in less than 10 seconds.

Here we are using the substitution method, so we need to substitute the each answer back to the question.

Please note A: B = 7:4 so the age of A has to be multiple of seven.

Look at the answer options

a.       12 is not a multiple of 7, so option a is rolled out.

b.      14 is a multiple of 7, after 5 years age will be 14+5=19.check it with the second ratio 11:7.here19 is not a multiple of 11, so the option b is rolled out.

c.       15 is not a multiple of 7, so option c is rolled out.

d.      Already three of the answer is eliminated we can say the option d is the correct answer.

28 is a multiple of seven and after 5 years 28+5 =33 is a multiple of 11.