diff --git a/1-js/02-first-steps/13-while-for/1-loop-last-value/solution.md b/1-js/02-first-steps/13-while-for/1-loop-last-value/solution.md
@@ -1,4 +1,4 @@
-The answer: `1`.

```js run
let i = 3;
@@ -8,18 +8,18 @@ while (i) {
}
```

-Every loop iteration decreases `i` by `1`. The check `while(i)` stops the loop when `i = 0`.

-Hence, the steps of the loop form the following sequence ("loop unrolled"):

```js
let i = 3;

-alert(i--); // shows 3, decreases i to 2

-alert(i--) // shows 2, decreases i to 1

-alert(i--) // shows 1, decreases i to 0

-// done, while(i) check stops the loop
```
diff --git a/1-js/02-first-steps/13-while-for/1-loop-last-value/task.md b/1-js/02-first-steps/13-while-for/1-loop-last-value/task.md
@@ -2,9 +2,9 @@ importance: 3

---

-# Last loop value

-What is the last value alerted by this code? Why?

```js
let i = 3;

diff --git a/1-js/02-first-steps/13-while-for/2-which-value-while/task.md b/1-js/02-first-steps/13-while-for/2-which-value-while/task.md
@@ -2,21 +2,21 @@ importance: 4

---

-# Which values does the while loop show?

-For every loop iteration, write down which value it outputs and then compare it with the solution.

-Both loops `alert` the same values, or not?

-1. The prefix form `++i`:

-    ```js
-    let i = 0;
-    while (++i < 5) alert( i );
-    ```
-2. The postfix form `i++`

-    ```js
-    let i = 0;
-    while (i++ < 5) alert( i );
-    ```
diff --git a/1-js/02-first-steps/13-while-for/3-which-value-for/solution.md b/1-js/02-first-steps/13-while-for/3-which-value-for/solution.md
@@ -1,17 +1,17 @@
-**The answer: from `0` to `4` in both cases.**

```js run
for (let i = 0; i < 5; ++i) alert( i );

for (let i = 0; i < 5; i++) alert( i );
```

-That can be easily deducted from the algorithm of `for`:

-1. Execute once `i = 0` before everything (begin).
-2. Check the condition `i < 5`
-3. If `true` -- execute the loop body `alert(i)`, and then `i++`

-The increment `i++` is separated from the condition check (2). That's just another statement.

-The value returned by the increment is not used here, so there's no difference between `i++` and `++i`.
diff --git a/1-js/02-first-steps/13-while-for/3-which-value-for/task.md b/1-js/02-first-steps/13-while-for/3-which-value-for/task.md
@@ -2,19 +2,19 @@ importance: 4

---

-# Which values get shown by the "for" loop?

-For each loop write down which values it is going to show. Then compare with the answer.

-Both loops `alert` same values or not?

-1. The postfix form:

-    ```js
-    for (let i = 0; i < 5; i++) alert( i );
-    ```
-2. The prefix form:

-    ```js
-    for (let i = 0; i < 5; ++i) alert( i );
-    ```
diff --git a/1-js/02-first-steps/13-while-for/4-for-even/solution.md b/1-js/02-first-steps/13-while-for/4-for-even/solution.md
@@ -1,5 +1,3 @@
-
-
```js run demo
for (let i = 2; i <= 10; i++) {
  if (i % 2 == 0) {
@@ -8,4 +6,4 @@ for (let i = 2; i <= 10; i++) {
}
```

-We use the "modulo" operator `%` to get the remainder and check for the evenness here.
diff --git a/1-js/02-first-steps/13-while-for/5-replace-for-while/solution.md b/1-js/02-first-steps/13-while-for/5-replace-for-while/solution.md
@@ -1,10 +1,7 @@
-
-
```js run
let i = 0;
while (i < 3) {
-  alert( `number ${i}!` );
  i++;
}
```
-
diff --git a/1-js/02-first-steps/13-while-for/5-replace-for-while/task.md b/1-js/02-first-steps/13-while-for/5-replace-for-while/task.md
@@ -2,13 +2,12 @@ importance: 5

---

-# Replace "for" with "while"

-Rewrite the code changing the `for` loop to `while` without altering its behavior (the output should stay same).

```js run
for (let i = 0; i < 3; i++) {
-  alert( `number ${i}!` );
}
```
-
diff --git a/1-js/02-first-steps/13-while-for/6-repeat-until-correct/solution.md b/1-js/02-first-steps/13-while-for/6-repeat-until-correct/solution.md
@@ -1,15 +1,14 @@
-
```js run demo
let num;

do {
-  num = prompt("Enter a number greater than 100?", 0);
} while (num <= 100 && num);
```

-The loop `do..while` repeats while both checks are truthy:

-1. The check for `num <= 100` -- that is, the entered value is still not greater than `100`.
-2. The check `&& num` is false when `num` is `null` or an empty string. Then the `while` loop stops too.

-P.S. If `num` is `null` then `num <= 100` is `true`, so without the 2nd check the loop wouldn't stop if the user clicks CANCEL. Both checks are required.
diff --git a/1-js/02-first-steps/13-while-for/6-repeat-until-correct/task.md b/1-js/02-first-steps/13-while-for/6-repeat-until-correct/task.md
@@ -2,12 +2,10 @@ importance: 5

---

-# Repeat until the input is correct

-Write a loop which prompts for a number greater than `100`. If the visitor enters another number -- ask them to input again.

-The loop must ask for a number until either the visitor enters a number greater than `100` or cancels the input/enters an empty line.
-
-Here we can assume that the visitor only inputs numbers. There's no need to implement a special handling for a non-numeric input in this task.

[demo]
diff --git a/1-js/02-first-steps/13-while-for/7-list-primes/solution.md b/1-js/02-first-steps/13-while-for/7-list-primes/solution.md
@@ -1,29 +1,29 @@
-There are many algorithms for this task.

-Let's use a nested loop:

```js
-For each i in the interval {
-  check if i has a divisor from 1..i
-  if yes => the value is not a prime
-  if no => the value is a prime, show it
}
```

-The code using a label:

```js run
let n = 10;

-nextPrime:
-for (let i = 2; i <= n; i++) { // for each i...

-  for (let j = 2; j < i; j++) { // look for a divisor..
-    if (i % j == 0) continue nextPrime; // not a prime, go next i
  }

-  alert( i ); // a prime
}
```

-There's a lot of space to optimize it. For instance, we could look for the divisors from `2` to square root of `i`. But anyway, if we want to be really efficient for large intervals, we need to change the approach and rely on advanced maths and complex algorithms like [Quadratic sieve](https://en.wikipedia.org/wiki/Quadratic_sieve), [General number field sieve](https://en.wikipedia.org/wiki/General_number_field_sieve) etc.
diff --git a/1-js/02-first-steps/13-while-for/7-list-primes/task.md b/1-js/02-first-steps/13-while-for/7-list-primes/task.md
@@ -2,16 +2,14 @@ importance: 3

---

-# Output prime numbers

-An integer number greater than `1` is called a [prime](https://en.wikipedia.org/wiki/Prime_number) if it cannot be divided without a remainder by anything except `1` and itself.

-In other words, `n > 1` is a prime if it can't be evenly divided by anything except `1` and `n`.

-For example, `5` is a prime, because it cannot be divided without a remainder by `2`, `3` and `4`.

-**Write the code which outputs prime numbers in the interval from `2` to `n`.**

-For `n = 10` the result will be `2,3,5,7`.
-
-P.S. The code should work for any `n`, not be hard-tuned for any fixed value.
-Original file line number
+Diff line change
@@ Expand Up / @@ -2,9 +2,9 @@ importance: 3 @@
     ---
-    # Last loop value
-    What is the last value alerted by this code? Why?
     ```js
     let i = 3;
@@ Expand Down @@