Question

If 3, 7 and 21 are the second, third and fourth terms of a proportion, respectively,
then find the first term.​

Answer 1

Answer:

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Step-by-step explanation:

Let the first number be x

So, Numbers proportion are x,3,7,21,

According to proportionality,

Product of means = Product of extremes

x:3::7:21

⇒$\frac{x}{3} = \frac{7}{21}$

Cross multiply,

x = 7 × 3 / 21

x = 21/21

x=1

Therefore, the required first number is 1

Answer 2

Answer:

Answer is 9

Step-by-step explanation:

Product if extream = Product of means

i.e x:3 :: 7:21

= x * 21 = 3 * 7

= x = 3 * 7 by 21

= x = 9