Times-Table Challenge I

Review — the Monster Maker 5 min

The Monster Maker is finished. Three things from it come back today.

• Each part was a costume. (costume [number v]) told us which one it wore.
• change [color v] effect by (25) changed a part without a new costume.
• go to [front v] layer put a part on top of the others.

Quick-fire

The random-monster button chose a head for you. Which block let the program choose?

Today’s Topic 3 min

• ((3) * (4)), ((3) + (4)) and ((9) - (4)) — Scratch does the sums
• (pick random (1) to (10)) — numbers nobody chose
• (join (a) (join [ × ] (b))) — a question made of numbers
• <(answer) = ((a) * (b))> — Scratch checks the answer

Learning outcome

By the end of this lesson you will be able to:

1. Use the green maths blocks to work out a number.
2. Make a new question every time with pick random and join.
3. Check a typed answer, and give the right one when it is wrong.

Learnt — a question nobody wrote 28 min

1 · Scratch can do sums

In Level 1 your quiz knew one answer. You typed it in yourself. Today Scratch works the answer out.

1. Click Operators. It is the green drawer.
2. Drag out (() * ()) into the Script Area.
3. Click the left circle and type 7. Click the right circle and type 8.
4. Click the block itself, not the circles.
5. A small bubble pops up under it. It says 56.

((7) + (8))
              

((15) - (8))
              

((7) * (8))
              

These round blocks report a number. So you can drop one into any round hole — a say block, a set block, even another green block.

when flag clicked
say ((7) * (8)) for (2) seconds
say ((7) + (8)) for (2) seconds
say ((15) - (8)) for (2) seconds
            

2 · Numbers nobody chose

A quiz with the same question every time is boring. Let the program pick the numbers.

We need somewhere to keep them, so we make two variables. In maths the two numbers are often called a and b, so we use those names.

1. Click Variables, then Make a Variable.
2. Type a, keep For all sprites, press OK.
3. Do it again for b.
4. Drag out set [a v] to (0).
5. Drop (pick random (1) to (10)) from Operators into its circle.
6. Do the same with a second set block for b.

set [a v] to (pick random (1) to (10))
set [b v] to (pick random (1) to (10))
            

3 · Glue the question together

The question has three pieces: a, the sign, and b. The (join [apple ] [banana]) block only glues two. So we put a join inside a join.

1. Drag a (join [apple ] [banana]) into the Script Area.
2. Drag a second join into its right-hand hole.
3. Drop (a) into the first hole.
4. In the middle hole type a space, then ×, then a space.
5. Drop (b) into the last hole.

say (join (a) (join [ × ] (b))) for (2) seconds
            

Put it all in a loop, and the Wizard makes up five questions by himself.

when flag clicked
repeat (5)
  set [a v] to (pick random (1) to (10))
  set [b v] to (pick random (1) to (10))
  say (join (a) (join [ × ] (b))) for (2) seconds
  say (join [The answer is ] ((a) * (b))) for (2) seconds
end
            

4 · Scratch checks the answer

Now the Wizard asks instead of says. You met ask [What's your name?] and wait in the Quiz Show. The question goes in its white hole, and the join fits there too.

To check, compare (answer) with ((a) * (b)). You never type the right answer in. Scratch works it out every time.

when flag clicked
set [a v] to (pick random (1) to (10))
set [b v] to (pick random (1) to (10))
ask (join (a) (join [ × ] (b))) and wait
if <(answer) = ((a) * (b))> then
  say [Correct!] for (2) seconds
else
  say (join [Not quite. The answer is ] ((a) * (b))) for (3) seconds
end
            

Why do we need a and b at all?

Why not put pick random straight into the question? Try it. It goes wrong in a sneaky way.

ask (join (pick random (1) to (10)) (join [ × ] (pick random (1) to (10)))) and wait
if <(answer) = ((pick random (1) to (10)) * (pick random (1) to (10)))> then
  say [Correct!] for (2) seconds
end
            

A variable remembers the number. The question and the check both read the same a and the same b, so they always agree.

Basic — a five-question round 25 min

Build one question and test it. Only then wrap it in a loop.

Step 1 — the room

1. Start a new project and delete the cat.
2. Choose the Chalkboard backdrop.
3. Add the Wizard sprite. Drag him to the left of the board.

Step 2 — three variables

1. Make score, a and b, all For all sprites.
2. Leave score ticked, so it shows on the Stage.
3. Untick a and b if you like. The game still works.

Step 3 — one question

1. On the Wizard, start with when flag clicked.
2. Add the two set blocks with pick random.
3. Add the ask block with the join inside it.
4. Add an if / else with <(answer) = ((a) * (b))>.
5. Press the flag. Answer right once, then wrong once.

Step 4 — five questions

1. Wrap everything under the hat in repeat (5).
2. Above the repeat, add set [score v] to (0).
3. In the top half of the if, add change [score v] by (1).

Step 5 — the score

1. Under the repeat, add a say block.
2. Build the sentence with a join inside a join.
3. Play the whole round twice. Once well, once badly.

when flag clicked
set [score v] to (0)
repeat (5)
  set [a v] to (pick random (1) to (10))
  set [b v] to (pick random (1) to (10))
  ask (join (a) (join [ × ] (b))) and wait
  if <(answer) = ((a) * (b))> then
    change [score v] by (1)
    say [Correct!] for (1) seconds
  else
    say (join [Not quite. It is ] ((a) * (b))) for (2) seconds
  end
end
say (join [You scored ] (join (score) [ out of 5])) for (4) seconds
            

The sevens

Practise one times table only — the 7 times table.

• Every question starts with 7.
• The other number goes from 1 to 12.
• Ten questions, and the score says “out of 10”.

when flag clicked
set [score v] to (0)
set [a v] to (7)
repeat (10)
  set [b v] to (pick random (1) to (12))
  ask (join (a) (join [ × ] (b))) and wait
  if <(answer) = ((a) * (b))> then
    change [score v] by (1)
    say [Correct!] for (1) seconds
  else
    say (join [Not quite. It is ] ((a) * (b))) for (2) seconds
  end
end
say (join [You scored ] (join (score) [ out of 10])) for (4) seconds
            

An adding round

Turn your round into a plus round, with bigger numbers.

• Both numbers go from 10 to 50.
• The question shows a + sign.
• A wrong answer still shows the right sum.

set [a v] to (pick random (10) to (50))
set [b v] to (pick random (10) to (50))
ask (join (a) (join [ + ] (b))) and wait
if <(answer) = ((a) + (b))> then
  change [score v] by (1)
else
  say (join [Not quite. It is ] ((a) + (b))) for (2) seconds
end
            

The missing number

Turn the question around. Show the answer, and hide one of the numbers.

• The question looks like “6 × ? = 42”.
• Scratch works out the 42 by itself.
• The player types the missing number.
• A wrong answer says what the missing number was.

set [a v] to (pick random (2) to (10))
set [b v] to (pick random (2) to (10))
ask (join (a) (join [ × ? = ] ((a) * (b)))) and wait
if <(answer) = (b)> then
  change [score v] by (1)
  say [Correct!] for (1) seconds
else
  say (join [The missing number was ] (b)) for (2) seconds
end
            

You choose how many

Before the first question, ask the player how many questions they want.

• The round asks exactly that many questions.
• The last line says “out of” that number.
• It works for 3, and it works for 12.

when flag clicked
ask [How many questions?] and wait
set [rounds v] to (answer)
set [score v] to (0)
repeat (rounds)
  set [a v] to (pick random (1) to (10))
  set [b v] to (pick random (1) to (10))
  ask (join (a) (join [ × ] (b))) and wait
  if <(answer) = ((a) * (b))> then
    change [score v] by (1)
  end
end
say (join [You scored ] (join (score) (join [ out of ] (rounds)))) for (4) seconds
            

Summary 4 min

Today the program stopped needing you to write its questions.

1. The green blocks ((a) + (b)), ((a) - (b)) and ((a) * (b)) do the sums.
2. (pick random (1) to (10)), kept in a variable, makes a new question each time.
3. A join inside a join glues numbers and signs into one question.
4. <(answer) = ((a) * (b))> checks the answer with the same numbers the question used.

Reporter

A round block that gives back a number or a word.

Random

Picked by the computer. You cannot guess it.

Join

Glues two pieces of writing into one.

Operator

A green block that does maths or compares things.

Next lesson: sixty seconds on the clock, three lives, and a round that ends by itself.