Question:
Gill has recently moved to a new house, which has a three- digit number. the sum of this number and its three individual digits is 429. What is the product of the three digits which make up the house number?

Answers:
A) 20 B)28 C)30 D)36 E)48

Please could you show me how to work this out

From Megan
Year 8 Student

Megan,

Start by observing that the number must be in the 410's or in the 420's. If it is in the 410's then the last digit, call it d, must satisfy 410 + 2d + 5 = 429. If it is in the 420's d must satisfy 420 + 2d + 6 = 429.