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Let us translate the sentences to mathematics for ease!
A 3-digit number
Ones digit → ( let p represent is )
Hundreds digit is four more than ones digit → ( 4 + p )
Tens digit is twice hundreds digit → 2 ( 4 + p ) = 8 + 2p
Sum of the digits is 12
↓
Hundreds digit + Tens digit + Ones digit = 12
( 4 + p ) + ( 8 + 2p ) + p = 12
Combine like terms
4 + 8 + p + p + 2p = 12
12 + 4p = 12
Take 12 to the opposite side { Do subtraction when you see addition }
12 ( - 12 ) + 4p = 12 - 12
4p = 0
Divide by 4 on either side
p = 0
( 4 + 0 ) + ( 8 + 2 ( 0 ) ) + ( 0 )
The number is 480
Check
Hundreds + Tens + Ones = 12
4 + 8 + 0 = 12
12 = 12
Let us translate the sentences to mathematics for ease!
A 3-digit number
Ones digit → ( let p represent is )
Hundreds digit is four more than ones digit → ( 4 + p )
Tens digit is twice hundreds digit → 2 ( 4 + p ) = 8 + 2p
Sum of the digits is 12
↓
Hundreds digit + Tens digit + Ones digit = 12
( 4 + p ) + ( 8 + 2p ) + p = 12
Combine like terms
4 + 8 + p + p + 2p = 12
12 + 4p = 12
Take 12 to the opposite side { Do subtraction when you see addition }
12 ( - 12 ) + 4p = 12 - 12
4p = 0
Divide by 4 on either side
p = 0
( 4 + 0 ) + ( 8 + 2 ( 0 ) ) + ( 0 )
The number is 480
Check
Hundreds + Tens + Ones = 12
4 + 8 + 0 = 12
12 = 12