MHB Struggling to solve number pattern question Please help

[yiannicart]

Hi,
I am in my final year of Secondary Teaching, specialising in history and language, so mathematics isn't always my strong point.:p
I tutor middle school students for extra money, and am helping one through a number reasoning test.

The question is as follows:

The numbers in each of the three brackets follow the same rule. Find the missing number.
[19, 25, 3] [4, 26, 11] [?, 51, 9]

A. 20
B. 31
C. 33 (the correct answer)
D. 34I cannot seem to find how 33 is the correct answer (I only know via the answer book), let alone the rule/pattern the numbers are following. If anyone can explain this to me and shed some light on this, it would be extremely helpful for me and for my student.
Cheers,
Yianni :D

 

[Greg]

Hi yiannicart and welcome to MHB! :D

It appears that the third number is half the difference between the first and second numbers:

(25 - 19)/2 = 3, (26 - 4)/2 = 11, (51 - 33)/2 = 9.

 

[yiannicart]

Hi yiannicart and welcome to MHB! :D

It appears that the third number is half the difference between the first and second numbers:

(25 - 19)/2 = 3, (26 - 4)/2 = 11, (51 - 33)/2 = 9.

Hi greg1313,
Thank you so much! This helps so much!
Kindest regards from Australia!
Yianni