GCSE maths question is impossible to answer without 'cheat code' formula

 GCSE exam season isn't far away, and maths students need to make sure they've got this formula in their back pocket. If you're gearing up to take your GCSEs in the next couple of months, or you're a parent of a teenager who is, you'll know that right now, revision is the most important thing.

Students will have been taught everything they need to know for their exams, but retaining that knowledge isn't always easy - especially when it comes to things like specific maths formula. One maths GCSE question being shared on social media is leaving people scratching their heads as they struggle to work it out, but it can be made so much easier just by using one very easy formula that you need to remember for your exam.

Saadat, a GCSE maths, English, and science tutor, shared the question in a TikTok video and said that many students end up losing "easy marks" on their exams as a result of forgetting the formula.

The question concerned interior angles. In an exam, this topic will usually come up in a question that gives you a shape with some information about some of the interior angles. You will then have to work out the value of another of the angles using the information you've been given.

In the question shared on TikTok, the shape was an irregular pentagram, with five angles of varying sizes. The following information is provided to work out the value of Angle A: "Angle A is the same as Angle C. Angle B is 155 degrees. Angle D is three times Angle C. Angle E is two times Angle C."

This might look impossible to solve, but if you remember one formula, you'll be able to solve any questions like this in no time - and you'll either ace your exam, or you'll be able to help your child get to grips with their revision much faster.

What you need to know is that the sum of all the internal angles is equal to (n-2) x 180.

In that equation, "n" is the number of angles the shape has. So in the question given in the video, the sum would be (5-2) x 180, or more simply, 3 x 180, which is 540.

So, now you know that all the angles in the shape have to add up to a total of 540, can you work out the value of Angle A?

Answer

Angle A is 55.

You should start the question by labelling the angles correctly. You know that A and C are the same, so you can write A for both. You also know the value of D is three times that of A, and E is twice the value of A, while the value of B is provided, at 155 degrees.

Writing this out as a full sum using the formula we learnt earlier, you can write: A + A + 3A + 2A + 155 = 540. To make this even simpler, you can condense all the A values until you're left with: 7A + 155 = 540.

Take the 155 away from 540, and your sum now reads: 7A = 385. All that's left to do is divide 385 by 7, either by using a calculator if you're allowed one in your exam or any other method you've learnt for division, and you should find that A is equal to 55.