If ab = 5, bc = 10 and cd = 13, then ad =

Question

If a*b = 5, b*c = 10 and c*d = 13, then a*d =

A. 650

B. 65

C. 26

D. 50/13

E. 13/2

IanStewart · Answer

Multiplying ab and cd, we get abcd = (5)(13). Now dividing abcd by bc will leave us with ad, so ad = (5)(13)/10 = 13/2.

AndySams · Answer

Given
ab=5
bc=10
cd=13

Then
ad=?
Step 1
ab=5
solving for a, a=5/b

Step 2
cd=13 
solving for d, d=13/c

Step 3
a*d=(5/b)*(13/c)=65/bc

Step 4
Given bc=10
substitute into 65/bc
65/10

Step 5
Cancel 5 in the numerator and the denominator
resulting in 13/2

Answer Choice E

Prasannak · Answer

Easiest way of solving this that i found is :
 (a*b*c*d) / (b*c) = a*d 
i.e (13*5)/10 = 13/2

NujNuj1 · Answer

The easiest way for me was:

Given
ab=5
bc=10
cd=13

then c and d have to be 13 or 1, but since something multiplied by 13 cannot equal 10, looking at bc=10, then d must equal 13 and c must be 1,

Then since c is 1, b must be 10, and if b is 10, then a must be 1/2, so therefore ad =13/3

Prep Toolkit