Question

What will come in place of the question mark (?) in the following number sequence?

17, 9, ?, 16.5, 35, 90

• A. 5
• B. 10
• C. 20
• D. None of these

Answer 1

The correct option is B 10

Let's try to understand how we got 9 from 17.
$17\times 0.5+0.5=9$
Now in this equation, we are multiplying 17 with 0.5 and 0.5 is then added to the product. The result is 9. Let's call 0.5 - the multiplying factor.
Same logic is used to get the next numbers in the sequence with multiplying factors being increased every time by a difference of 0.5.
$9\times 1+1=10$
$10\times 1.5+1.5=16.5$
$16.5\times 2+2=35$
$35\times 2.5+2.5=90$