N14: estimate answers; check calculations using approximation and estimation, including answers obtained using technology

Given that 43 × 16 = 688, find the answer to:

1) 688 ÷ 16

2) 1.6 × 4300

3) Estimate 68.8 ÷ 4.3

4) 68.8 ÷ 4.3

1) 688 ÷ 16 = 43

2) 1.6 × 4300 = 6880 (16 was divided by 10, 4300 was multiplied by 100, overall change was x10 to give 6880)

3) 70 ÷ 5 = 14 (use the simplest numbers possible - 70/4 is harder)

4) 68.8 ÷ 4.3 = 16 (both sides were divided by 10 so the answer doesn’t change from the original sum)

What is estimation?

A rough calculation used to make answering problems easier

Estimate 7.1×97

7×100=700

Isla uses her mobile phone while abroad. She received 3 minutes of calls at 88p per minute. She made 7 minutes of calls at 71p per minute. She sent 4 text messages at 52p per message. Estimate the total cost.

3×90=270, 7×70=490, 4×50=200

270+490+200=960p or £9.60

702.1 + 299.3/1.9 × 5.1

700+300=1000, 2×5=10

1000/10=100

(4.022 +√102)/0.51

4+10=14, 14×2=28

√(50.77/0.513)

50×2=100

√100=10