how many two digit number have 10 digit smaller than the unit digit
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Answered by
3
Answer:
36
Step-by-step explanation:
(8 starting with 1) + (7 starting with 2) + (6 starting with 3) +... + ( 1 starting with 8)
= 8 + 7 + 6 + 5 + 4 + 3 + 2 + 1
= 8 × 9 / 2
= 4 × 9
= 36
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