Angles around a point 100, 150, x

Step by step

The question

Question: find x when the angles around a point are 100°, 150° and x.

1 Use the angle fact

Angles around a point add up to 360°.

That is one full turn.

So we add them all and make it 360: 100 + 150 + x = 360.

2 Group like terms

The plain numbers go together.

Now we have 250 + x = 360.

3 Remove the 250

We want x by itself.

The 250 is in the way.

To remove 250, we take away 250.

We do it on both sides.

Why both sides?

The = sign means both sides are the same amount.

If we change only one side, they are not the same any more.

250 and − 250 make zero.

Cross them out.

360 minus 250 is 110.

So x = 110.

The angle x is 110°.

4 Check

Let's check: put x = 110 back and add the angles.

They add up to 360°.

So x = 110 is right!

Let's look back.

First: use the angle fact.

Then: group like terms.

Then: remove the 250.

Last: check.