Question 1098477: the sum of two number is 13 twice the first number added to thrice the second number is 21, find the Two numbers Answer by ikleyn(52908) (Show Source):
You can put this solution on YOUR website! . The sum of two number is 13. Twice the first number added to thrice the second number is 21, find the two numbers.
Answer. First number is 18. The second number is -5.
Check. a) 18 + (-5) = 13. Correct. b) 2*18 + 3*(-5) = 36 - 15 = 21. Correct.
Solution
1. Since "the sum of two number is 13 ", then
twice the sum of two numbers is 26.
In addition, according to the condition,
2. Twice the first number added to thrice the second number is 21.
It implies immediately that the second number is 21 diminished by 26, i.e. -5.
3. Having it, everybody can easily conclude that the first number is 18.
Solved.
I specially constructed the solution in this way to show that it can be solved MENTALLY, without writing and using equations.
