Given that

a:b = 2:3 and b:c = 4:5.

The LCM of 3 and 4 is 12

On multiplying the first ratio by 4 and the second by 3 so that ‘b’ will be the same on both.

So, a:b = 8:12 and b:c = 12:15.

Now ‘b’ is common, we will combine the ratios.
a:b:c = 8:12:15.

Let us combine bridge a:b:c with c:d, holding‘c’ as the common element.

LCM of 15 and 6 is 30

On multiplyinf a:b:c by 2 and c:d by 5 to get c=30.

Again on combining we get

a:b:c = 16:24:30 and c:d = 30:35.

Hence a:b:c:d = 16:24:30:35.