CBSE Class 3 Mathematics NCERT Solutions: Chapter 7 - Time Goes On

Solution: The story contains several incorrect time-related words. By replacing them with the correct words from the given options, the story becomes logical. Here are the corrections:

1. "sets" should be "rises" (The sun rises in the morning, not sets when someone wakes up).
2. "evening" should be "morning" (Sumana wakes up when the sun rises, which is morning).
3. "hours" should be "minutes" (Washing face takes a few minutes, not hours).
4. "months" should be "days" (Watching eggs for a nest usually takes days, not months).
5. "week" should be "moment" (A cat jumping onto a tree is a quick event, a moment, not a week).
6. "days" should be "seconds" (An object falling after being hit happens very quickly, in seconds, not days).
7. "year" should be "week" (A mango needing more time to ripen might need a week, not a whole year).
8. "dinner" should be "breakfast" (Upma is typically eaten for breakfast, not dinner, especially after waking up in the morning).

The corrected story reads:

As the sun rises Sumana wakes up. What a lovely morning! She washes her face fast in 2 minutes and runs out. She goes straight to the bird's nest. She has been watching the eggs for the last few days. She was waiting for the baby birds to come out. But before she can blink her eyes, in a moment a cat jumps on the tree. The mother bird cries loudly and Sumana rushes to shoo away the cat. As the cat jumps, it hits the big green mango. Dhum!

In two seconds it is on the ground! Oh, how sad! The mango is still not fully ripe. It needed one more week to become sweet. Suddenly Sumana's sister calls out— Are you still not hungry? Has your stomach clock gone to sleep? Come and eat hot upma for breakfast.

Solution: Here is a table categorizing various activities based on the approximate time they take:

Takes minutes

• A bath
• To boil milk
• To sharp a pencil
• To blow a balloon
• To eat an apple
• To wear shoes
• To cook ladyfinger
• To fill petrol in car

Takes hours

• To stitch a shirt
• To knit a sweater
• A school day
• To bake cake
• To paint your house
• Dusting of house

Takes days

• To set curd
• To weave a sari
• For a banana to become ripe
• For seed to germinate
• To make furniture
• To change from day to night

Solution: Here is a list of activities categorized by how long they take, including very fast (seconds) and very slow (months) ones:

Takes seconds

• To blink my eyes
• To snap my fingers
• To gulp my medicine
• To throw a ball
• To take a snap (photo)

Takes months

• To grow wheat (from seed to big plant)
• To change from summer to winter
• For a baby to come out of its mother's stomach
• To write a book
• To construct a house

Solution: Most people are capable of performing simple, simultaneous actions like speaking and stamping their feet at the same time. This involves coordinating two different motor and vocal functions, which is generally achievable for young children.

Answer: Most of us can speak and stamp at the same time.

Solution: Let Irfan's age be represented by the variable 'x' years. According to the problem, his mother's age is twice his age, so her age is $2x$ years. Also, his mother is 20 years older than him, so her age is $x\; +\; 20$ years. Since both expressions represent the mother's age, we can set them equal to each other: $$2x\; =\; x\; +\; 20$$ To solve for x, subtract x from both sides of the equation: $$2x\; -\; x\; =\; 20$$ $$x\; =\; 20$$ So, Irfan's age is 20 years. Now, we find the mother's age using either expression: Mother's age = $2x\; =\; 2\; \backslash times\; 20\; =\; 40$ years. Or, Mother's age = $x\; +\; 20\; =\; 20\; +\; 20\; =\; 40$ years. Both calculations give the same result.

Answer: Irfan's age is 20 years and his mother's age is 40 years.

Solution: Information regarding Bincy's birth certificate was not included in the provided text. To answer questions related to a birth certificate, the actual certificate details (like date of birth, place of birth, parents' names, etc.) are required. Without this information, it is impossible to proceed with any analysis or answer specific questions about it.