Question

c varies jointly with a and b.
when a = 2 and b = 3, c = 42.
what is the value of c when a = 4 and b = 5?
a. 140
b. 35
c. 50.4
d. 252

Explanation:

Step1: Define joint variation formula

$c = k \cdot a \cdot b$ (k is constant)

Step2: Calculate k using given values

$42 = k \cdot 2 \cdot 3 \implies k = \frac{42}{6} = 7$

Step3: Find c when a=4, b=5

$c = 7 \cdot 4 \cdot 5 = 140$

Answer:

A. 140