Hello?
Probability
Level
2
How many seven digit phone numbers begin with 432 and end with 3 or 5?
1790
2300
1920
2000
2250
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1 solution
Moderator note:
Simple standard approach.
The fourth digit can be selected from 10 possible choices 0,1,2,3......9.The same is true for the fifth and the sixth digit. the seventh digit can be picked in two ways; it can be either three or five.According to the rule of product,the number of such phone is 10 x 10 x 10 x 2 = 2000