Can you solve an example without a convenient calculator?

Solving interesting problems not only helps to have fun, but also allows you to pump your thinking abilities. And this is especially necessary for an adult, because he, unlike schoolchildren, does not solve problems every day. But the brain must somehow keep in good shape, make it work regularly. Then he will be ready at any time and in any situation to find a solution.

So today's editorial office. "Site" I ask readers to solve some interesting problems. Try to do without using a calculator on your smartphone, deciding only on your own. Can you handle each of our tasks correctly?



Solving interesting problems

1. As a first task, we offer a fairly simple (at first glance) example. It seems that any student can cope with this. But in reality, adults often get confused when they see several arithmetic actions at once, and do not know what to solve and in what sequence.
   
   
   
   
2. Next, we offer a more complicated example, because there are brackets that can confuse everyone who at one time was frivolous to math lessons. Can you make no mistakes to give the right answer?
   
   
   
   
3. And finally, we offer a problem, the conditions of which are indicated in the picture. What would be the total age of four friends in 8 years if they were 100 years old in 12 years? An interesting problem, the solution of which is not as obvious as it may seem.
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Tips to challenges

1. First we do multiplication and division, and then addition and subtraction. Then our example 6 – 1 * 0 + 2 / 2 will take the following form 6 – 0 + 1 = 7. It's pretty easy to decide if you remember the school rules.
   
   
   
   
2. First we do things in brackets and then everything else. Therefore, the example 6 * 3 - 3 * (20 / 4) turns into 18 - 3 * 5 = 18 - 15 = 3. It seems that everything is right. Or did you get a different answer?
3. As for the problem, first we suggest to find out how old four friends are now. Over the next 12 years, each friend will be 12 years older. Therefore, the total age of friends today is 100 – (4 * 12) = 52 years. Then in 8 years their total age will be 52 + (4 * 8) = 84 years. Or could a solution be found in a simpler way?
   
   
   
   

Don’t forget to write your answers in the comments. And also note what task you had the most trouble with. Did you manage to do this without using a calculator?