+1839 Find the sum of all positive integers less than $1000$ ending in $3$ or $4$ or $5$.
+399 We want all numbers in this form:
_ _ 3
_ _ 4
_ _ 5
An integer can't be part of both groups, since an integer has only one ending number.
For all of these, the first two can cycle from 10 to 99 which is 90 numbers
Sum of numbers ending in 3 is (sum of numbers 10 - 99) * 10 + 90*3 = 49320
Sum of numbers ending in 4 is (sum of numbers 10 - 99) * 10 + 90*4 = 49410
Sum of numbers ending in 5 is (sum of numbers 10 - 99) * 10 + 90*5 = 49500
49320 + 49410 + 49500 = 148230.
