Question

if 1/8 of a pencil is black,1/2 of the remaining is white and the remaining,3/2cm is blue,find the total lenth of the pencil

Answer 1

Let total length of pencil be x cm.
Then, black part = x/8
Remaining part pencil after black part = x - x/8 = 7x/8
then White part = 1/2 (7x/8) 
= 7x/16
Now Remaining part of pencil is blue = total length of pencil - (length of black part + length of white part)
length of blue part of pencil = x - (x/8 + 7x/16)
length of blue part of pencil = x - (2x + 7x)/16
length of blue part of pencil = x - 9x/16
length of blue part of pencil = (16 x - 9x)/16
∴ Length of blue part = 7x/16;

According to question
Length of blue part = 31/2 
7x/16 = 31/2 
⇒ 7x/16 = 7/2
⇒ x/16 = 1/2
⇒ x = 16/2
∴ x = 8 cm

Answer 2

total X cm

black= x/8

remain= x-x/8=7x/8

white=1/2(7x/8)=7x/16

● 7x/16=7/2

x=8cm