Solution
1) For every 12 photos, the printer takes 4 minutes
Therefore for 1 photo, the printer will take 4/12 minutes = 1/3 minutes
Hence in 6 minutes, the printer will print 6 /1/3 = 6 x 3 = 18 photos
For 21 photos the printer will take = 21 x 1/3 = 7 minutes
In 9 minutes, the printer will print 9/1/3 = 9 x 3 = 27 photos
For 30 photos the printer will take 30 x 1/3 = 10 minutes
So we will now draw the table
2) Brand A has 24 pencils that cost $7.49
Brand B has 28 pencils that cost $9.97
The unit price of Brand A = 7.49/24= $0.31208333 = $ 0.31
The unit price of Brand B = 9.97/28 = $0.3560714 = $ 0.36
28 pencils for brand A will cost 28 x 0.31 =$8.68
Hence brand A is better than brand B because 28 pencils of brand A are cheaper than 28 pencils of brand B and the unit price of a pencil of brand A is cheaper than that of brand B.
Brand A is better
