Let us look closely at the picture provided above.
You see a single straight baseline at the bottom and two rays shooting upward from the same point.
The image challenges us with a bold rule at the top: “No pen! No paper!!”
That means we need to solve this entire problem in our heads using simple logic.
The big question at the bottom asks: “What is the missing angle?”
To find the answer, we only need to remember one fundamental rule about straight lines.
A completely straight line always forms a total angle of 180 degrees.
Now, let us analyze the information given in the drawing step by step.
We have a straight line split into three connected angles at a central vertex.
The angle on the far left side is given as 130 degrees.
The angle on the far right side is given as 100 degrees.
The middle angle marked with a red question mark is the mystery angle we need to calculate.
Notice how these angles overlap with each other along the straight line.
Let us break down the left side first.
The angle on the left measures 130 degrees, which stretches from the far-left baseline up to the second ray.
Since the total straight line is 180 degrees, the remaining angle on the far right outside this 130-degree piece must be 180 minus 130, which equals 50 degrees.
So, the small section on the far right is 50 degrees.
Now, let us look at the right side of the diagram.
The angle on the right measures 100 degrees, stretching from the far-right baseline to the first ray.
We already know that the small section on the far right is 50 degrees.
Since this 100-degree angle includes both the middle red question mark angle and that 50-degree rightmost section, we can subtract to find the middle angle.
We calculate 100 degrees minus 50 degrees, which gives us 50 degrees.
Alternatively, we can solve it by looking at the remaining section on the left.
The right-side angle is 100 degrees, leaving the far-left section as 180 minus 100, which equals 80 degrees.
Since the total angle covering the left and middle sections is 130 degrees, we subtract the far-left 80 degrees from 130 degrees.
130 degrees minus 80 degrees equals 50 degrees.
Another simple mental math method is to add the two overlapping given angles: 130 degrees plus 100 degrees equals 230 degrees.
Since a straight line is only 180 degrees, the extra amount comes entirely from the middle angle being counted twice.
We simply subtract the straight line’s total of 180 degrees from 230 degrees.
230 degrees minus 180 degrees equals 50 degrees.
No matter which logical path you follow, the result is always the same.
The missing angle marked by the question mark is exactly 50 degrees!
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