SOLUTION: a two-digit number is twice the sum of its digits. if the tens digit is 7 less than the unit digit. find the number

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Question 273605: a two-digit number is twice the sum of its digits. if the tens digit is 7 less than the unit digit. find the number
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Call the units digit u
and the tens digit t
given:
10t+%2B+u+=+2%2A%28t+%2B+u%29
t+=+u+-+7
---------------
Substitute
10%2A%28u+-+7%29+%2B+u+=+2%2A%28u+-+7+%2B+u%29
10u+-+70+%2B+u+=+2u+-+14+%2B+2u
11u+-+4u+=+70+-+14
7u+=+56
u+=+8
t+=+u+-+7
t+=+8+-+7
t+=+1
The number is 18
check:
10t+%2B+u+=+2%2A%28t+%2B+u%29
10%2A1+%2B+8+=+2%2A%281+%2B+8%29
10+%2B+8+=+2%2A9
18+=+18
OK