Multiply 40x7 then subtract that total you got from multiplying 40x7 with 420
40x7=160
420-160=260
260 pieces of wood were left.
The best way to multiply complicated problems mentally* is to break them into chunks.
Start with 20 times 8 to get 160, and then 8 times 5 to get 40. Add these together to get 200. 200 times 3 is 600, and 20 times 200 is 4000. Add these together to get your final answer, 4600.
In other words 8 x 20 + 8 x 5 = 200 200 x 3 + 200 x 20 = 4600
*I assumed you meant mentally, because otherwise you'd just multiply longhand, multiplying two of the three numbers and then multiplying their product with the third.
10.5 and 8.4 ......................,,,,,
Answer:
a. b=4
Step-by-step explanation:
From the attached triangle drawn below:
NL=20, LM=3b, 
Since we are told that:
The correct option is A.
