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Explanation:
n = number of new flash cards practiced
2n = number of old flash cards practiced
The 2n is due to the fact that the number of old flash cards is double that of the new ones (eg: 10 is twice that of 5).
The two expressions must add to 45.
new + old = total
n + 2n = 45
3n = 45
n = 45/3
n = 15
2n = 2*15 = 30
Noah practiced 15 new flash cards and 30 old flashcards which is a total of 15+30 = 45. This confirms our answer.
Also note that the ratio of new to old is 15:30 which reduces to 1:2, then we can multiply both sides by 5 to get 5:10. This effectively shows that 15:30 and 5:10 are the same equivalent ratio (just in different forms). This helps confirm our answer.
