Find the fourth proportional to 7, 13 and 21.
Show answer & explanation
Correct answer: C
Explanation
The correct answer is Option 3 i.e. 39.
Calculations:
Three numbers are given 7, 13, and 21.
If a, b, c, and d are in proportional series then a/b = c/d
Let the fourth proportional be x.
⇒ 7/13 = 21/x
⇒ x = (21 × 13)/7 = 39