Posted by **jessica meyz** on Wednesday, August 5, 2009 at 6:01am.

how many positive four- digit integers have 3 as their tens digit and 5 or 9 as their ones digit?

i don't know where to begin

- Mathematics -
**drwls**, Wednesday, August 5, 2009 at 6:14am
Start listing them. Four-digit numbers must be between 1000 and 9999. The last two numbers must be 35 or 39.

1035

1039

1135

1139

...etc., ending with

9935

9939.

There are 90 pairs of numbers, starting with 10 and ending with 99 as the first two digits.

90 pairs = 180

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