2019 AIME II Problem 3

Below is the professionally curated solution for Problem 3 of the 2019 AIME II, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2019 AIME II solutions, or check the answer key.

All of the real AMC 8, AMC 10, AMC 12, and AIME problems in our complete solution collection are used with official legal permission of the Mathematical Association of America (MAA).

Concepts:prime factorizationfactor counting

Difficulty rating: 1950

3.

Find the number of 77-tuples of positive integers (a,b,c,d,e,f,g)(a, b, c, d, e, f, g) that satisfy the following system of equations: abc=70,abc = 70, cde=71,cde = 71, efg=72.efg = 72.

Solution:

Since 7171 is prime, in cde=71cde = 71 one of the three factors is 7171 and the other two equal 1.1. But cc divides abc=70abc = 70 and ee divides efg=72,efg = 72, and 7171 divides neither 7070 nor 72.72. So c=e=1c = e = 1 and d=71.d = 71.

The system reduces to ab=70ab = 70 and fg=72.fg = 72. Each divisor aa of 7070 determines b,b, giving τ(70)=8\tau(70) = 8 ordered pairs, and likewise τ(72)=12\tau(72) = 12 ordered pairs (f,g).(f, g). The total is 812=96.8 \cdot 12 = 96.

← Problem 2Full ExamProblem 4

Problem 3 in Other Years