Question

A children's book has dimensions 20 cm by 24 cm.

What scale factor should be used to make an enlarged version that has dimensions 25 cm by 30 cm?

A. 5
B. 1.5
C. 1.25
D. 0.8

Answer 1

C. 1.25

25/20 = 1.25
30/24 = 1.25

Thus, it is a scale of 1.25

Answer 2

We should use C. 1.25

Explanation:

We know that the children's book dimensions are 20 cm x 24 cm

We need to find a scale factor (which is a number) that will turn the dimensions 20 cm x 24 cm ⇒ 25 cm x 30 cm

We can write :

(20 cm) . a = 25 cm

Where ''a'' is the scale factor.

Solving for a :

`(20cm).a=25cm\\a=(25cm)/(20cm)=1.25 \\a=1.25`

This result is reasonable because the scale factor won't have units

A scale factor of 1.25 turns 20 cm ⇒ 25 cm

We can use the another dimension to verify :

(24 cm) . a = 30 cm

(24 cm) . (1.25) = 30 cm

30 cm = 30 cm

The scale factor is option C. 1.25