Mathematics—the subject that proudly has its own fan following has also broken many studious hearts, frustrated many young minds and acted difficult for most students. If studying this subject is a nightmare for you, then you have come to the right place. Did you know that competitive exams such as CAT, GMAT and IIT-JEE focus majorly on mental math? You can’t definitely be sitting in the exam hall, clueless and panicked, while solving questions that can be answered mentally.
Mobile learning apps such oustme.com offer a range of 2-minute quizzes comprising 5 questions—which means this requires the students to answer quickly yet smoothly. Team Oust presents to you a list of easy hacks to make mental calculation seem like a cakewalk to you. Have a look:
Sum a series of even numbers
Example 1: 2+4+6+…+100
- Divide the highest number in the series by 2 (100/2=50)
- Multiply the result of step 1 by itself plus 1 (50×51=2550)
Example 2: 2+4+6+…+128
- Divide the highest number in the series by 2 (128/2=64)
- Multiply the result of step 1 by itself plus 1 (64×65=4160)
Sum a series of odd numbers (Example 1+3+5+…+123)
Example 1: 1+3+5+…+123
- Add 1 to the highest number in the series (123+1=124)
- Divide the answer to step one by 2 (124/2=62)
- Square the answer to step 2 (62^2=3844)
Example 2: 1+3+5+…+135
- Add 1 to the highest number in the series (135+1=136)
- Divide the answer to step one by 2 (136/2= 68)
- Square the answer to step 2 (68^2=4624)
Square any two digit number
Example 1: 43^2
- Square each digit and place the numbers side by side (4^2 next to 3^2=1609)
- Multiply the digits of the number being squared (4×3=12)
- Double the answer in step 2 and add a zero (240)
- Add steps 1 and 3 together (1609+240=1849)
Example 2: 85^2
- Square each digit and place the numbers side by side (8^2 next to 5^2=)6425
- Multiply the digits of the number being squared (8×5=40)
- Double the answer in step 2 and add a zero (800)
- Add steps 1 and 3 together (6425+800=7225)
Square any number ending in 5
- Multiply the first digit by itself plus one (6×7=42)
- Place the number 25 on the end (4225)
- Multiply the first digit by itself plus one (3×4=12)
- Place the number 25 on the end (1225)
Multiply any 2 two-digit numbers up to 20×20
Example 1: 17×12
- Add the one’s place digit from the smaller number to the larger number (17+2=19)
- Add a zero to the end (190)
- Multiply the ones digit of the two numbers (7×2=14)
- Add steps 2 and 3 (204)
Example 2: 15×11
- Add the one’s place digit from the smaller number to the larger number (15+1=16)
- Add a zero to the end (160)
- Multiply the ones digit of the two numbers (5×1=5)
- Add steps 2 and 3 (165)
Square Root Approximation
The easiest way to find the square root of any number is through the method of close approximation.
Let’s try this hack for 85:
Step1: Find the closest previous square (81) and the next square (100).
Step2: Find the difference between the 85 and 81=4
Step3: Divide 4 by (100-81)=4/19=0.21
Step4: Add the result from 0.21+9=9.21
To handle tough multiplication problems
Have a larger number to multiply and one of the numbers is odd, then you can certainly subdivide to calculate the correct answer:
- 64 x 225 = 8 x 450 = 4 x 900 = 3600
This looks easy, isn’t? It is!
2. Want to subtract a large number such as 647 from 1000?
Do it like this:
Step1: subtract 6 from 9=3
Step2: subtract 4 from 9=5
Step3: subtract 7 from 10=3
Your answer will be=353
Practice these hacks on your own regularly—no matter which topic you are tackling with at the moment. Class tests, competitive exams and home assignments will become a lot easier to take if your mental math is strong.
Makes sense, right?
To challenge yourself further, download the Oust App now and get started!