MENTAL MATHS CLASS 6

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43. An elevator descends at 7 m/min from 5 m above ground to –205 m. How long will it take?

Total distance = 5 + 205 = 210 m
Time = 210 ÷ 7 = 30 minutes

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44. Sum of two integers = –1500; one is 599. Find the other.

Let the other integer be x:
599 + x = –1500
x = –1500 – 599 = –2099

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45. Find the value of 125 – 200 ÷ 8 + 5 × 25

Follow BODMAS:

• 200 ÷ 8 = 25

• 5 × 25 = 125

Now:
125 – 25 + 125 = 225

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46. Garvit earns ₹2 profit per pen, loses ₹0.50 per pencil. Earns ₹10 from 15 pens. How many pencils?

Profit from 15 pens = 15 × 2 = ₹30
Total profit = ₹10
So loss from pencils = 30 – 10 = ₹20
Let pencils = x
Loss: 0.50 × x = 20 → x = 20 ÷ 0.5 = 40 pencils

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47. Additive inverse of (–12 + 16 – 42 ÷ (3/7)) × (–2)(–3)(–4)

First solve inside:

• 42 ÷ (3/7) = 42 × (7/3) = 98

• –12 + 16 – 98 = –94

Now product: (–2)(–3)(–4) = –24

Total: –94 × –24 = 2256

Additive inverse = –2256

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48. From number line, find additive inverse of (A – B – C), where A=4, B=2, C=–3

A – B – C = 4 – 2 – (–3) = 4 – 2 + 3 = 5
Additive inverse of 5 = –5

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49. Elevator started at 5th floor: +4 –6 +9 –5

5 + 4 = 9
9 – 6 = 3
3 + 9 = 12
12 – 5 = 7th floor

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50. Product of 3 integers = –900; Two are +25 and –6; Find third

25 × (–6) = –150
–900 ÷ –150 = 6

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✅ Final Answers Summary:

43. 30 minutes

44. –2099

45. 225

46. 40 pencils

47. –2256

48. –5

49. 7th floor

50. 6