1950 AMC 12 Problem 7

Attempt Problem 7 of the 1950 AMC 12 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1950 AMC 12 solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

If the digit

1

is placed after a two digit number whose tens’ digit is

t,

and units’ digit is

u,

the new number is:

10t+u+1

100t+10u+1

1000t+10u+1

t+u+1

None of these answers

The original two digit number is

10t+u

Appending a digit multiplies the original number by

10

before adding that digit

The two digit number is

10t+u.

Placing

1

after it produces

\begin{aligned} &10(10t+u)+1\\ &=100t+10u+1. \end{aligned}

Thus, the correct answer is B.

Problem 7 in other years