Question

What must be added to each of 7, 16, 43 and 79 so that they become proportion ?

• A. 2
• B. 5
• C. 6
• D. 7

Answer 1

The correct option is B

5

Let x be added to each of 7, 16, 43 and 79 so that the resulting number are in proportion. i.e., (7 + x) : (16 + x) : : (43 + x) : (79 + x)

$\frac{(7+x)}{(16+x)}=\frac{(43+x)}{(79+x)}$
(7 + x)(79 + x) = (16 + x)(43 + x)
553 + 7x + 79x + x² = 688 + 16x + 43x + x²
553 + 86x + x² = 688 + 59x + x²
86x – 59x + x² – x² = 688 – 553
27x = 135
$x=\frac{135}{27}=5$
The numbers are: (7 + 5), (16 + 5), (43 + 5) and (79 + 5)
i.e. 12, 21, 48 and 84.