GMAT math thinking skills 3

Topic: Number system

Difficulty level: Average

You will get word problems like this in your exams.

The concepts involved in this problem are

1. Equations

2. Numbers system

Method 1:

This method will take time as you need to read the question,  write equations, and solve them. Time consuming!!

First: assume variables

Let John’s age (at the time of the wedding) be J and Mary’s age (at the time of the wedding) be M. 

Second : write equations

The condition relating their ages is

Hence Mary was 18 and John was 24, when they got married 

That was long and time consuming.

Now let us  try approach 2

Method 2:

The previous approach involves equations. Some of us

• don’t like solving equations
• tend to make errors while solving equations..

There is an easier and faster approach  

Lets observe equation 1

M =(3/4)J                      Re-arranging ............(M/3) = (J/4)

we can observe that ages are integers. 

We can say that M is divisible by 3 and J is divisible by 4.

Similarly   

Lets observe equation 2

12 years hence

(M+12)/5 =(J+12)/6

(M+12) is divisible by 5 and (J+12) is divisible by 6

Let us use the answer options and eliminate the wrong options

Mary’s age when she got married should be one of the 5 options

(A) 24       (B) 26         (C) 18        (D) 30          (E) 22  

Mary’s age,when she got married, should be divisible by 3

Hence we can eliminate option B,E as these numbers are not divisible by 3

Further 

Mary’s age, after 12 years, should be divisible by 5

Let us take each option

 Option A: Mary’s age initially 24……after 12 years………. Mary’s age = 36

 Option C: Mary’s age initially 18……after 12 years ………Mary’s age = 30

 Option D: Mary’s age initially 30……after 12 years …….. Mary’s age = 42

Only 30 is divisible by 5

Hence option C should be the correct answer

Therefore, Mary’s age at the time of her wedding should be 18.

Isn't the second method easy and fast… However many test aspirants don’t observe these subtleties.

Most of us start writing equations when we see word problems.

Take-away:

observe the numbers, check the nature of the numbers( prime/odd/even/ divisible by x numbers….)

Watch this tutorial video and understand mathematical reasoning skills..

You can excel in math once you learn these skills.

Need math help: Get in touch with me:

My linkedin profile: https://www.linkedin.com/in/georgeanand

My facebook learning group:  https://www.facebook.com/groups/semanticsGMAT

My company: http://www.semanticslearning.com/

Want to explore math reasoning skills further try another problem

Click here

Solution here:

https://letsgmat.blogspot.com/2020/06/gmat-math-thinking-skills-1.html