72
Four: 8, 26, 44 and 62.
10
Answer 18. The two digit numbers less than 50 whose digits add to 9 are 45, 36, 27 and 18. 36 and 18 are even. 36 is the only number whose paired factor with 2 is even (18).
Not too sure of the question but how about 0.77775
solution: we know that there are 25 prime numbers are between 1-100 and 168 prime numbers less than 1000. 100 x 100=10000(5 digits) 999 x 999=998001(6 digits) 1000 x 1000=1000000(7 digits) so our answer should be same as the number of prime numbers between 100 to 999. hence, 168-25=143. 143 prime numbers will be there less than 1000 whose square has 5 or 6 digits.
754 Piece of cake!
There are nine(9) numbers: 19, 28, 37, 46, 55, 64, 73, 82, 91
All of them. We normally count in decimal numbers and therefore all digits in decimal numbers must be less than ten.
There are 5 numbers of 1 digit, 25 numbers of 2 digits, and 75 numbers of 3 digits. This makes 105 numbers in all.
I look at it this way:-- There are 90,000 numbers with five digits. (100,000 minus 10,000 with less than 5 digits)-- If the sum of the first 5 digits is odd, it can be made even by using 1, 3, 5, 7, or 9for the 6th digit ... 5 choices.-- If the sum of the first 5 digits is even, it remains even by using 2, 4, 6, 8, or 0for the 6th digit ... 5 choices.-- So, for any one of the 90,000 five-digit numbers, there are 5 choices for the 6th digitthat result in an even sum of all six.-- So, there must be 450,000 suitable 6-digit numbers.
Fifteen.
114 beacause it's three digits a factor of seven even
64