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 By: geniuskids (offline)  Saturday, May 04 2013 @ 10:52 AM CDT (Read 973 times)
geniuskids

Q9) Joshua is studying for a Science test. He has read 1/4 of the textbook. After reading another 15 pages, the number of pages he has read became 2/3 of the number of pages left unread. How many pages did Joshua read?

My ans is wrong despite using model! Help!

Thanks

Active Member

Registered: 11/12/11
Posts: 169

 By: echeewh (offline)  Sunday, May 05 2013 @ 08:12 PM CDT
echeewh

Hi genuiskids,

Following is my worked solution:

*** - for alignment purpose

|-------|-------|-------|-------|
<-- R --><------ UR ----->
<-- 2p --><------ 3p ----->

R : UR
2 : 3 **** {2p : 3p}

R = (1/4) total + 15 = 2p

From the model, split (1/4) total into 5u each (since we need to convert this total of (4/4) into 5p).

Hence, total = 4 × 5 = 20u
So 1p = 20u ÷ 5 = 4u

(1/4) total + 15 = 2p
5u + 15 = 2 × 4 = 8u
3u --> 15
1u --> 5

Pages read (R) = 8u --> 8 × 5 = 40

-------------

<Alternative method>

Given that R : UR is 2 : 3 , this infers that (2/5) total of book was read (after reading another 15 pages).

So (1/4) total + 15 = (2/5) total
(2/5) total - (1/4) total = 15
(8/20) total - (5/20) total = 15
(3/20) total = 15
(1/20) total = 5

Pages read (R) = (2/5) total = (8/20) total = 8 × 5 = 40

=========

Trust this helps.

Do let me know again if there's further clarification.

Cheers,
Edward

Active Member

Registered: 04/21/11
Posts: 627

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