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Question 137015: I would also appreciate it if someone could help me understand how to solve the following problem....thanx.
Question:
The sum of the digits in a certain three-digit number is 21. The sum of the first and third digits is twice the middle digit. If the hundreds and tens digits are interchanged, the number is reduced by 90. Find the number.
Answer by scott8148(6628)   (Show Source):
You can put this solution on YOUR website! let h="hundreds digit", t="tens digit", an u="units digit"
"sum of the digits in a certain three-digit number is 21" __ h+t+u=21
"sum of the first and third digits is twice the middle digit" __ h+u=2t
__ substituting __ t+2t=21 __ t=7
__ substituting __ h+7+u=21 __ h=14-u
" If the hundreds and tens digits are interchanged, the number is reduced by 90" __ 100h+70+u=700+10h+u+90
subtracting 70+u and substituting __ 100(14-u)=700+10(14-u)+20 __ 1400-100u=700+140-10u+20 __ 540=90u __ 6=u
substituting __ h=14-6 __ h=8
876 is the number
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