Question

Logs are stored in apile of 20 rows,with each row having one fewer log than the one below it. If there is 48 logs on the bottom row how many logs are in the pile?

​

Answer 1

770

Explanation:

1st raw =a = 48

2nd raw = 47

.

.

d= -1 , n = 20

Summation S= n/2 [2a+(n-1)d]

= 20/2 [ 2×48 + (20-1)×-1]

= 770

Answer 2

754 logs

Explanation:

If you are starting at 48 logs on the bottom row subtracting one log for each row you go up, then you should have 28 logs in the top row.

This is because 48-20=28

now you need to find the factorial of 48 starting at 28.

Factorial is like 1+2+3+4+5=15. So it is basically just adding every single whole number that are in between 2 whole numbers.

So for this equation you would need to do: 28+29+30+31+32+33+34+35+36+37+38+39+40+41+42+43+44+45+46+47+48= 754.

:) Hope that helped!