Question

A bag contains blue marbles and red marbles, 21 in total. The number of blue marbles is 9 less than 2 times the number of red marbles. How many blue marbles are there?

pls help

Answer 1

11 marbles.

Explanation:

Given: Total number of marbles= 21.

The number of blue marbles is 9 less than 2 times the number of red marbles.

Now, finding the number of blue marbles.

Lets assume the number of red marbles be "x".

∴ number of blue marbles=
`(2* x-9)`= (2x-9)

As given total number of marbles is 21.

we can write,
`x+ (2x-9)= 21`

Opening parenthesis.

⇒
`3x-9= 21\ marbles`

Adding 9 on both side.

⇒
`3x= 30`

cross multiplying both side

∴ x=
`(30)/(3) = 10\ marbles`

Red marbles= 10 marbles.

Now, subtituting the number of red marbles to find number of blue marbles.

Blue marbles= (2x-9)

Number of blue marbles=
`( 2* 10-9)= 20-9`

∴ Number of blue marbles= 11 marbles.