Find the fourth term of the sequence

Question

Here is a question I found in a grade 7 math book...

Chose the correct number to the blank

9, 4, 10, 11, ...... , 26

(a) 16 (b) 18 (c) 24 (d) 32

Thanks

Answer 1

This isn't any arithmetic, or geometric progression as you would expect. It's rather a simple sequence following the pattern:

$$T_n + T_{n+1} - 3 = T_{n+2} $$

Therefore,

$T_5$ = $T_3 + T_4 - 3 = 10 + 11 - 3 = 18 $