=> Single digit numbers: 1, 3 or 5: Three numbers => Two–digit numbers: Units digit = 1, 3 or 5. For the tens’ digit, there are 5 choices {anything apart from what went into the units digit}. So, there will be 3 × 5 = 15 such numbers. => Three–digit numbers: Units digit = 1, 3 or 5. For the tens’ digit, there are 5 choices {anything apart from what went into the units digit}. For the 100s’ digit, there are 4 choices {anything apart from what went into the units digit or tens digit}. So, there will be 3 × 5 × 4 = 60 such numbers. => 4–digit numbers: There will be 3 × 5 × 4 × 3 = 180 numbers. => 5–digit numbers: There will be 3 × 5 × 4 × 3 × 2 = 360 numbers. => 6–digit numbers: There will be 3 × 5 × 4 × 3 × 2 × 1 = 360 numbers. Total number of numbers = 360 +360 + 180 + 60 + 15 + 3 = 978. Correct Answer : 978
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