Spicy number

Algebra Level 1

A 2-digit number is called spicy if it equals the sum of its digits added to the product of its digits. For example, 69 = 6 + 9 + 6 × 9 , 69 = 6 + 9 + 6\times 9, so 69 is a spicy number.

What is the second largest spicy number?

Note: "second largest" refers to the second spicy number if they were ranked from largest to smallest.


The answer is 89.

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2 solutions

Siddharth Singh
Nov 23, 2015

Let the number be 10 x + y 10x+y and its digits be x x and y y .

( x y ) + ( x + y ) = 10 x + y (x*y)+(x+y)=10x+y

\Rightarrow x y + x + y = 10 x + y xy+x+y=10x+y

\Rightarrow x y 9 x = 0 xy-9x=0

\Rightarrow x ( y 9 ) = 0 x(y-9)=0

\Rightarrow x = 0 x=0 or y = 9 y=9

Since , x = 0 x=0 gives a 1-digit number,so y = 9 y=9 and x x can any values between 1 1 and 9 9 .

Second largest spicy number is 89 \boxed{89} .

Some idiot has put this question up on Facebook asking for the next smallest spicy number, and then once you submit the right answer for that quetion and get it wrong, you notice the questions don't match. How stupid is that?

Ian Turnbull - 5 years, 6 months ago

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Internet is full of idiots, can't trust nobody.

A Former Brilliant Member - 5 years, 6 months ago

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Hi Matheus, yes I'm an idiot too, I keep thinking that a maths site's personnel would get something simple like asking questions right first time, or at least proof read stuff before they publish it. Yeah I know, idiot!

Ian Turnbull - 5 years, 6 months ago

umm not 79? 7+9+(7x9)= 16+63=79 isn't that how this is suppose to work?

William Graf - 5 years, 6 months ago

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According to the formula for a 2-digit number, spicy #s are 19, 29, 39...99. Since 99 is the highest, the second highest is 89.

Brett Manley - 5 years, 6 months ago

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smacks forehead remind me to not do these at 1 am. Confuse largest and next smallest number

William Graf - 5 years, 6 months ago

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@William Graf They posted on facebook saying 69 is the smallest whats the second smallest

Mike Durkin - 5 years, 6 months ago

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@Mike Durkin 79 would be the 2nd smallest. Not 89.

Peter Formaini - 5 years, 6 months ago

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@Peter Formaini Yea I was just noting that they posted a different question on fb so if he followed that link and didn't look at this question ... it would be 79

Mike Durkin - 5 years, 6 months ago

A more generalized version of this problem: link

Nihar Mahajan - 5 years, 6 months ago

Same way...

Dev Sharma - 5 years, 6 months ago

10 6 + 9 = 6 + 9 + 6 9 Hence, 10 x + y = x + y + x y; where x = 1,2,3,...,8,9

Once this is simplified, 9 x = x y Since x is not equal to zero, y = 9

Therefore it can be concluded that this so called spicy number is valid for all 2 digit numbers which end up with 9 such as 19,29,39,...,89,99

Madhawa Balasuriya - 5 years, 6 months ago

How do you consider 69 is the smallest such number? I think the statement is false. Smallest is 19

Md Islam - 4 years, 11 months ago

Almost perfect as a solution except that x is not equal to zero. x is indeterminate which is why the solution works for every positive value of x and zero. Interestingly it also works for negative numbers of x but since y must be positive it prevents the solution 10x + y to be a valid representation of the two digit number.

Rob Bednarik - 4 years, 11 months ago

if digits are x, and y and the number is 2digits, then the number is 10x + y so the equation is: 10x + y= x + y + xy y is on both sides so we can cancel y off resulting in: 10x= x+ xy 10x= x(1 +y) 10= y+1 y= 9 x= any number from 1-9 So largest spicy number=99 Second= 89

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