Question 71286
The sum of the digits of the two-digit numeral is 8. The number with the digits interchanged is 7 times the tens digit of the original number. Find the original number 
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Let the two digit number be tu where t is the "ten's" digit and u and the "unit's digit.  Also keep in mind that tu =10t+u just like 23 = 10*2+3.
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EQUATIONS:
t+u=8
10u+t = 7t
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Solve the 1st for t: t=8-u
Siplify the 2nd then,
Substitute t=8-u into the 2nd:
10u=6t
10u=6(8-u)
10u = 48-6u

16u=48
u=3
The t=8-u=8-3=5
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The original number is 53
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Cheers,
Stan H.