SOLUTION: A shop has 48 notebooks for sale. The number of blue notebook is 12 less than twice the number of red notebooks. How many blue notebooks are there?

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Question 1025047: A shop has 48 notebooks for sale. The number of blue notebook is 12 less than twice the number of red notebooks. How many blue notebooks are there?
Found 2 solutions by josmiceli, addingup:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +a+ = number of blue notebooks
Let +b+ = number of red notebooks
-----------------
(1) +a+%2B+b+=+48+
(2) +a+=+2b+-+12+
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Substitute (2) into (1)
(1) +2b+-+12+%2B+b+=+48+
(1) +3b+=+60+
(1) +b+=+20+
and
(2) +a+=+2b+-+12+
(2) +a+=+2%2A20-+12+
(2) +a+=+40+-+12+
(2) +a+=+28+
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There are 28 blue notebooks
---------------
check:
(2) +a+=+2b+-+12+
(2) +28+=+2%2A20+-+12+
(2) +28+=+40+-+12+
(2) +28+=+28+
OK

Answer by addingup(3677) About Me  (Show Source):
You can put this solution on YOUR website!
b+r = 48 (1)
b = 2r-12 Use this value for b in equation (1):
2r-12+r = 48 add 12 on both sides and add r on left:
3r = 60
r = 20 There are 20 red notebooks and the problem says:
b = 2r-12 = 2(20)-12=40-12= 28 There are 28 blue notebooks