# How to Improve Your Mental Maths Skills December 8, 2021

Mental maths is a key skill to have in any situation, regardless of whether you are taking PSLE Maths, Secondary Maths, or JC Maths. While some papers allow you to bring your own calculator, Maths tutors still recommend avoiding overreliance on calculators, both for the papers where calculators are not allowed, and also so that you will not have to waste time keying a simple equation into your calculator. Regardless, mental sums help sharpen your mind and can come in handy even when you’re not in the examination hall – you can use your mental maths skills when making a purchase, converting currency in a foreign land, calculating the fastest route to a destination, and so on. Read on to learn some tips you can use to strengthen your mental maths skills that will help you in your PSLE Maths or JC Maths paper.

## Use Round Numbers

If you are dealing with “not-so-nice” numbers – such as a number that does not end in “5” or “0” – calculating a simple addition or subtraction can seem challenging. If you need to calculate 427 + 503, an easier way instead of trying to add the numbers up front would be to shift the 3 from 503 over to 427, giving you 430 + 500. This makes it much more straightforward to add the two numbers since they are both multiples of tens, giving you the result of 930.

You can also use a similar method for an addition such as 298 + 350. Most students hesitate for a moment when they see 98 added to 50 since it is not a straightforward calculation. Instead, you can simplify the calculation by adding 2 to 298 to round it off to 300, and then adding 300 and 350 to get 650. From this number, subtract the extra 2 you added earlier, resulting in the correct answer of 648.

This technique can apply to any type of calculation, not just addition or subtraction. If you need to multiply 39 by 5, you can round 39 off to 40 by adding 1. Multiply 40 by 5 to get 200, then subtract the extra 5 (from the 5 times that you added 1 to 39) from the answer to getting 195. It’s usually easier to do mental calculations with numbers that are multiples of 10, so make use of this to round your numbers off and calculate them faster.

## Learn Quick Multiplication Tricks

You can always memorize the times table, but calculating any multiplications beyond that can be difficult, especially if the multiplication involves two or more multiple-digit numbers. What’s the product of 34 and 19? Most people may have to think for a while about that.

One of the easiest multiplications to calculate mentally is any number multiplied by 10. All you have to do is add a 0 to the end of the number and you’ll get your result. For example, to calculate 12345 x 10, just add a 0 to the number which will give you 123450.

Although it is slightly more complicated than multiplying by 10, you can also calculate any number multiplied by 11 with a trick. To multiply any single-digit number by 11, simply put the number side-by-side to form the two digits of the result – for instance, 5 x 11 is 55, and 6 x 11 is 66. For two-digit numbers, you can add the two digits of the number and insert this result in between the two digits. As an example, to multiply 15 by 11, take 1 + 5 which is 6, and put it in between 1 and 5, which gives you 165.

## Learn Divisibility Rules

To find whether a number is divisible by a certain single-digit number, you can follow these divisibility rules instead of going by trial and error, which can take up valuable time that you may not have in the exams.

• A number is divisible by 10 if it ends in 0.
• A number is divisible by 9 if its digits are added together and this result can be divided by 9.
• A number is divisible by 8 if it ends in 000 or its last three digits can be divided by 8.
• A number is divisible by 7 if you remove its last digit, double that digit, subtract it from the remaining number, and the result is divisible by 7.
• A number is divisible by 6 if it is even and the sum of its digits can be divided by 3.
• A number is divisible by 5 if it ends in 0 or 5.
• A number is divisible by 4 if its last two digits can be divided by 4.
• A number is divisible by 3 if the sum of its digits can be divided by 3.
• A number is divisible by 2 if its last digit is even (0, 2, 4, 6, or 8).