How many 3digit numbers have their hundreds tens and units in acsending order?
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ans:100-200--->123-129 total(7)
-->134-139(6)
--->145-149(5)
--->156-159(4)
-->167-169(3)
--->178-179(2)
-->189(1)
if we add 7+6+5+4+3+2+1=28
like this if we continue up to 999
then we get
28+21+15+10+6+3+1=84
so ans:84
-->134-139(6)
--->145-149(5)
--->156-159(4)
-->167-169(3)
--->178-179(2)
-->189(1)
if we add 7+6+5+4+3+2+1=28
like this if we continue up to 999
then we get
28+21+15+10+6+3+1=84
so ans:84
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