1÷( 1/ 10+ 1/ 15)=6
2. The ratio of A to B is 4:7, and the number of B minus A is 15. What's the number of B? (Similarly, the equation cannot be used ~)
15 \u( 7/ 1 1-4/ 1 1)= 55 55 x4/ 1 1 = 20 55 x7/ 1 1 = 35
3. A bug climbs from point A to point B, climbing 1.2 meters per minute, and it takes 48 minutes to get there. If its speed increases by 0.5 meters per minute, it can arrive a few minutes earlier (by arithmetic).
1.2x 48 = 57.6 57.6÷( 1.2+0.5)=≈33.9
4 Use the nine digits 1, 2, 3, 4, 5, 6, 7, 8, 9 as the minimum number and divide by the nine digits divisible by 1 1. What are these nine digits? (Equation is not allowed)
A positive integer divisible by 1 1 is characterized by:
The difference between the sum of numbers on odd digits and the sum of numbers on even digits can be divisible by 1 1.
Write down 123456789
The sum of numbers on odd digits = 1+3+5+7+9=25.
The sum of numbers on even numbers =2+4+6+8=20.
Adjust at the low level and try to keep the high level 1234 unchanged.
Sum of odd digits = 1+3+7+8+9=28.
The sum of numbers on even numbers =2+4+5+6= 17.
So the smallest number divisible by 1 1 is 123475869.