To find the denominator that would make the ratios proportional, we can use the concept of cross-multiplication.
Given: 21/3 = 49/?
To make these ratios proportional, we need to find a denominator for the second ratio that gives the same result when we cross-multiply.
To cross-multiply, we multiply the numerator of the first ratio by the denominator of the second ratio, and vice versa. In this case, it would be:
(21 * ?) = (3 * 49)
Now we need to find a number that makes the left side of the equation equal to the right side.
Let's solve for the missing value:
21 * ? = 3 * 49
Dividing both sides of the equation by 21:
? = (3 * 49) / 21
Simplifying:
? = 147 / 21
To reduce the fraction, we can divide the numerator and denominator by their greatest common divisor, which in this case is 21:
? = 7
So, to make the ratios 21/3 and 49/7 proportional, the denominator for the second ratio should be 7.