The ratio of the radii of two circles is 2:3. The diameter of the smaller circle is 15 mm. What is the length of the diameter of the larger circle?

We actaully don't need to convert the diameter to radius

15 is smaller, it is 2 units

larger is 3 units

15/2=7.5

7.5 times 3=22.5

answer is 22.5 mm

if you want to do it the long way

convert to radius

15mm/2=7.5mm, that is smaller radius

7.5/2=x/3

times both sides y 6

22.5=2x

divide both sides by 2

11.25=x

taht is radius

now double it for diameter

11.25*2=22.5

answer is still 22.5mm

2:3 15:x 2/3=15/x 2x = (15*3) (cross multiply) x=45/2 (divide both sides by2) x=22.5 Answer=22.5mm