Number Properties Puzzle – Challenge 17
Number Properties Puzzle - Challenge 17 is a multiple-choice math challenge from Effortless Math. Read the problem, choose from the answer options below, then open the solution to see the full step-by-step working and check your reasoning against it.
A FREE math puzzle for all ages! Sharing this fun math challenge with your kids is a good way to get them thinking mathematically.
Challenge:
How many numbers between 400 and 600 begin with digit 5 or end with digit 5?
A- 20
B- 100
C- 110
D- 120
E- 140
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The correct answer is C.
Numbers between 500 and 599 begin with 5. So, there are 100 numbers that begin with 5.
Consider numbers that end with 5:
405, 415, 425, 435, …, 495
Also, numbers 505, 515, 525, …, 595, end with 5. But, we counted them before!
There are 20 numbers that end with 5. We counted 10 of them before. Therefore, there are 100 + 10 = 110 numbers that begin with digit 5 or end with digit 5.The Absolute Best Books to Ace Algebra
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