Jabu had

Jabu had a few marbles. Today, he played and doubled his number. Then Thabo gave him three marbles for free. Jabu now has 21 marbles. How many did he have before he started playing? Solve this problem using a suitable model.

Correct answer:

n =  9

Step-by-step explanation:

2 n+3=21  2n=18  n=218=9  n=9

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