SOLUTION: The tens digit of a two digit number exceeds the unit digit by 4. If the product of the tens digit and the unit digit is 21, find the number

Question 936439: The tens digit of a two digit number exceeds the unit digit by 4. If the product of the tens digit and the unit digit is 21, find the number
Answer by TimothyLamb(4379) (Show Source): You can put this solution on YOUR website!
x = unit digit
y = tens digit
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y = x + 4
xy = 21
x(x + 4) = 21
xx + 4x - 21 = 0
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the above quadratic equation is in standard form, with a=1, b=4 and c=-21
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to solve the quadratic equation, by using the quadratic formula, copy and paste this:
1 4 -21
into this solver: https://sooeet.com/math/quadratic-equation-solver.php
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the quadratic has two real roots at:
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x = 3
x = -7
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the negative root doesn't fit the problem statement, so use the positive root:
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x = 3
y = x + 4
y = 3 + 4
y = 7
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answer:
the number = 73
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